Laboratory of Polymer Chemistry

Department of Chemistry

University of Helsinki

Finland

Solution Behavior of Responsive Cationic

Polymers

Erno Karjalainen

ACADEMIC DISSERTATION

To be presented, with the permission of the Faculty of Science of the University of

Helsinki, for public examination in Auditorium A129, Department of Chemistry,

on June 12th 2015, at 12 noon.

Helsinki 2015

Supervisor

Professor Heikki Tenhu

Laboratory of Polymer Chemistry

Department of Chemistry

University of Helsinki

Finland

Opponent

Professor André Laschewsky

Department of Chemistry

Universität Potsdam

Reviewers

Professor Kyösti Kontturi

Department of Chemistry

Aalto University

Dr. Janne Raula

NanoMaterials Group

Department of Applied Physics

Aalto University

ISBN 978-951-51-1177-7 (paperback)

ISBN 978-951-51-1178-4 (PDF)

https://ethesis.helsinki.fi/

Unigrafia

Helsinki 2015

Abstract

This thesis combines anion responsive polymeric ionic liquids (PILs) with

thermoresponsive polymers. The polymers have been synthesized with controlled radical

polymerization methods.

A water-insoluble PIL was used as a macro-chain transfer agent in synthesis of block

copolymers with poly(N-isopropyl acrylamide) (PNIPAm). PNIPAm chains of various

lengths were grown to the same PIL-block. These polymers show a lower cirical solution

temperature (LCST) type behavior, typical to PNIPAm. The PIL block and the PNIPAm

block interact strongly, no phase transition can be observed for the block copolymers with

short PNIPAm chains. The block copolymers form complex aggregates in water. The

hydrophobic PIL-homopolymer can be used to make stable particles in salt free water.

Also triblock copolymers with a long central PNIPAm block and short water soluble

PIL blocks were synthesized. These polymers also show interactions between the PIL and

PNIPAm blocks. This can be seen for example as reduced enthalpy of phase transition for

the triblock copolymers compared to the PNIPAm homopolymer. The triblock copolymers

form complex aggregates at elevated temperatures.

The LCST-type phase transtiton of weakly cationic poly(2-(dimethylamino)ethyl

methacrylate) (PDMAEMA) can be modified with bis(trifluoromethane)sulfonamide

(NTf2) ions. The presence of NTf2 induces also an upper critical solution temperature

(UCST) type transition for PDMAEMA, if the polymer is charged enough. NTf2 turns

PDMAEMA to a stronger base, presumably due to the effective screening of charges.

NTf2 induces an UCST-type transition for strong polycations in the presence of an

added electrolyte. The phase behavior of the polycation-NTf2 system can be influenced by

addition of sodium chloride. Similar transition can also be induced by

trifluoromethanesulfonate (OTf), though OTf is needed in much higher concetrations. This

allows the use of OTf as the only salt.

The NTf2-polycation interactions influence the phase behavior of copolymers of N-

isopropyl acrylamide (NIPAm) and strongly cationic (3-acrylamidopropyl)

trimethylammonium chloride (AMPTMA). With low AMPTMA content, the copolymers

show LCST-type behavior in the presence of NTf2 and a copolymer with high AMPTMA-

content shows UCST-type behavior. If NIPAm and AMPTMA are copolymerized in

nearly equal amounts, both transitions may coexist. The phase behavior of the copolymers

can be influenced by NaCl addition in all cases.

Acknowledgements

This work has been underway in the Laboratory of Polymer Chemistry for a long time. It

was made possible by Finnish Funding Agency for Technology and Innovation TEKES,

Academy of Finland, and ERA.Net RUS. Without their financial aid, my dreams would

never have become reality.

I wish to express my deep gratitude to my supervisor, Professor Heikki Tenhu. His

guidance over the years has been invaluable. Especially his great skill in writing has been

essential in the realization of the articles and this thesis. I am thankful for the great

freedom of research he has allowed.

I am thankful to Professor Kyösti Kontturi and Dr. Janne Raula for dedicating their

time to be the reviewers of my thesis. I am also grateful to Professor Kontturi for the

TEKES project.

My undying gratitude goes to Professor André Laschewsky for dedicating his time and

travelling to Finland to be my opponent.

The funding obtained by Dr. Vladimir Aseyev made the completion of this thesis

possible. I am forever obliged to him for this.

Seija Lemettinen, Heljä Heikkilä, Juha Solasaari, and Ennio Zuccaro are thanked for

their work of high importance in keeping the lab functional.

I wish to thank all the past and present members of the Laboratory of Polymer

Chemistry for the help and friendship over the years. I am especially thankful to Dr.

Mikko Karesoja for sharing the fume hood in a civilized manner over a number of years. I

wish also to thank Dr. Sami Hietala for the discussions about pop culture in particular,

about life in general, and occasionally about science too. I am grateful to Professor

Eduardo García-Verdugo for his valuable aid in numerous matters, including scientific

ones. The following members of the lab deserve special thanks: Petri, SP, Tommi,

Szymon, Helena, Lauri, Jukka, Teemu, Katriina, Lauri, Anu, Naveen, and the people I did

not remember right now.

I am thankful to all my friends. Especially Juha Jaakkonen is thanked for being a great

friend.

My parents, Marjaana and Esa, and my sister Emma deserve my deepest thanks for

more reasons that can be listed here. I thank also my in-laws, Irma and Aarni, for all the

help they have given.

Aura, my beloved, there are no words to describe the gratitude for all the love and

support you’ve given to me. And Saana, my little princess, you are a true wonder. For you

two, I dedicate all my work.

Erno Karjalainen

Helsinki, April 2015

Contents

Abstract 3

Acknowledgements 4

List of original publications 8

Abbreviations and Symbols 10

1. Introduction 14

1.1. Controlled Radical Polymerization 14

1.1.1. ATRP 14

1.1.2. RAFT 17

1.2. ILs and PILs 19

1.2.1. NTf2 and Other Hydrophobic Anions 20

1.2.2. Applications of PILs in Colloids 21

1.3. Thermoresponsive Polymers in Water 22

1.3.1. PNIPAm and the LCST Phenomenon 23

1.3.2. UCST 25

1.3.3. PDMAEMA and Quaternized PDMAEMA 26

1.3.4. Thermoresponsive PILs 27

1.3.5. PIL-PNIPAm Copolymers 28

1.3.6. Copolymers with Soluble-Insoluble-Soluble Transitions in Water 28

2. Objectives of This Study 30

3. Experimental 31

3.1. Syntheses 31

3.1.1. Block CopolymersI, II 31

3.1.2. Cationic HomopolymersIII, IV 33

3.1.3. Cationic Copolymers of NIPAmV 34

3.2. Characterization of the Polymers 35

3.3 Solution Properties 36

3.3.1. Sample Preparation 36

3.3.2. Transmittance MeasurementsII-V 36

3.3.3. CalorimetryI-III, V 37

3.3.4. Dynamic Light ScatteringI-III 38

3.3.5. Zeta potentialI, II 38

3.3.6. Cryo-EMI 39

4. Results and Discussion 40

4.1. Syntheses 40

4.1.1. Block CopolymersI, II 40

4.1.2. Cationic HomopolymersIII, IV 41

4.1.3. Cationic Copolymers of NIPAmV 42

4.1.4. Naming of the Polymers 42

4.2. Solution Properties of the PNIPAm and Its Block CopolymersI ,II, V 43

4.2.1. Enthalpy of Transition in Pure WaterI ,II, V 43

4.2.2. Block Copolymer AggregatesI, II 46

4.3. Counterion-Induced UCST in WaterIII-V 52

4.3.1. Effect of NTf2 on TcUIV, V 53

4.3.2. Effect of OTf on TcUIV 56

4.3.3. Reversibility of the Counterion-Induced UCST-transitionIV, V 59

4.4. Effect of LiNTf2 on LCST BehaviorIII, V 60

4.4.1. NTf2 and PDMAEMA-1 at Room TemperatureIII 60

4.4.2. Effect of LiNTf2 on Thermoresponsive Behavior of PDMAEMA-1III 63

4.4.3. Thermoresponsive Behavior of PDMAEMA with Varying pH and

Constant Concentration of LiNTf2 III 64

4.4.4. PNIPAm and LiNTf2V 66

4.4.5. Effect of LiNTf2 on TcL of CPsV 67

4.4.6. Effect of LiNTf2 on ΔHIII, V 71

5. Conclusions 75

6. References 76

8

List of original publications

This thesis is based on the following publications:

I Karjalainen, E.; Chenna, N.; Laurinmäki, P.; Butcher, S. J.; Tenhu, H.

Diblock copolymers consisting of a polymerized ionic liquid and poly(N-

isopropylacrylamide). Effects of PNIPAM block length and counter ion

on self-assembling and thermal properties. Polym. Chem. 2013, 4, 1014-

1024.

II Karjalainen, E.; Khlebnikov, V.; Korpi, A.; Hirvonen, S.; Hietala, S.;

Aseyev, V.; Tenhu, H. Complex interactions in aqueous PIL-PNIPAm-

PIL triblock copolymer solutions. Polymer 2015, 58, 180-188.

III Karjalainen, E.; Aseyev, V.; Tenhu, H. Influence of Hydrophobic Anion

on Solution Properties of PDMAEMA. Macromolecules 2014, 47, 2103-

2111.

IV Karjalainen, E.; Aseyev, V.; Tenhu, H. Counterion-Induced UCST for

Polycations. Macromolecules 2014, 47, 7581-7587.

V Karjalainen, E.; Aseyev, V.; Tenhu, H. Upper or lower critical solution

temperature, or both? Studies on cationic copolymers of N-

isopropylacrylamide. Polym. Chem. 2015, 6, 3074-3082.

The publications are referred to in the text by their roman numerals.

The author’s contribution to the publications:

The author synthesized all the polymers discussed in this thesis. The author wrote all the

manuscripts in collaboration with the coauthors. For articles I and II, the author

participated in drawing the research plan and conducted a major part of the experimental

work. For articles III-V, the author drew the research plan and conducted all the

experiments.

9

In addtition to this thesis, the author has contributed to several other publications:

VI Karesoja, M.; Jokinen, H.; Karjalainen, E.; Pulkkinen, P.; Torkkeli, M.;

Soininen, A.; Ruokolainen, J.; Tenhu, H. Grafting of montmorillonite

nano-clay with butyl acrylate and methyl methacrylate by atom transfer

radical polymerization: Blends with poly(BuA-co-MMA). J. Polym. Sci.,

Part A: Polym. Chem. 2009, 47, 3086-3097.

VII Hirvonen, S.; Karesoja, M.; Karjalainen, E.; Hietala, S.; Laurinmäki, P.;

Vesanen, E.; Butcher, S. J.; Tenhu, H. Colloidal properties and gelation of

aqueous dispersions of conductive

poly(benzimidazobenzophenanthroline) derivatives. Polymer 2013, 54,

694-701.

VIII Witos, J.; Karesoja, M.; Karjalainen, E.; Tenhu, H.; Riekkola, M. Surface

initiated polymerization of a cationic monomer on inner surfaces of

silica capillaries: Analyte separation by capillary electrophoresis versus

polyelectrolyte behavior. J. Sep. Sci. 2013, 36, 1070-1077.

IX Karesoja, M.; McKee, J.; Karjalainen, E.; Hietala, S.; Bergman, L.; Linden,

M.; Tenhu, H. Mesoporous silica particles grafted with

poly(ethyleneoxide-block-N-vinylcaprolactam). J. Polym. Sci., Part A:

Polym. Chem. 2013, 51, 5012-5020.

X Privalova, E. I.; Karjalainen, E.; Nurmi, M.; Mäki-Arvela, P.; Eränen, K.;

Tenhu, H.; Murzin, D. Y.; Mikkola, J. Imidazolium-Based Poly(ionic

liquid)s as New Alternatives for CO2 Capture. ChemSusChem 2013, 6,

1500-1509.

XI Karjalainen, E.; Izquierdo, D. F.; Marti-Centelles, V.; Luis, S. V.; Tenhu, H.;

García-Verdugo, E. An enzymatic biomimetic system: enhancement of

catalytic efficiency with new polymeric chiral ionic liquids synthesized

by controlled radical polymerization. Polym. Chem. 2014, 5, 1437-1446.

XII Karesoja, M.; Karjalainen, E.; Hietala, S.; Tenhu, H. Phase Separation of

Aqueous Poly(2-dimethylaminoethyl methacrylate-block-N-

vinylcaprolactams). J. Phys. Chem. B 2014, 118, 10776-10784.

10

Abbreviations and Symbols

[CTA]0 Initial concentration of a CTA

[I]0 Initial concentration of an initiator

[M]0 Initial concentration of a monomer

ACPA Azobis(cyanopentanoic acid)

AGET ATRP Activators generated by electron transfer for

ATRP

AIBN Azobis(isobutyronitrile)

AMPTMA (3-acrylamidopropyl) trimethylammonium

chloride

ARGET ATRP Activators regenerated by electron transfer for

ATRP

ATRA Atom transfer radical addition

ATRP Atom transfer radical polymerization

Block-1 and Block-2 Poly(3-methyl-1-(4-vinylbenzyl)-1-imidazolium

chloride)-block-poly(N-isopropyl acrylamide)-

block-poly(3-methyl-1-(4-vinylbenzyl)-1-

imidazolium chloride)

ClMeSt p-chloromethylstyrene

CNT Carbon nanotube

conv Conversion of the monomer

CP Copolymer of AMPTMA and NIPAm

CPA (4-Cyanopentanoic acid)-4-dithiobenzoate

CPDTC 2-cyano-2-propyldodecyl trithiocarbonate

CTA Chain transfer agent

d Average number of dead chains produced by a

termination event

DEA Diethyl acrylamide

DEDBrA Diethyl meso-2,5-dibromoadipate

DHB 2,5- dihydroxy benzoic acid

DLS Dynamic light scattering

DMAEMA 2-(dimethylamino)ethyl methacrylate

DMF Dimetylformamide

DPT Targeted degree of polymerization

DPtheor Theoretical degree of polymerization

EClPr Ethyl 2-chloropropionate

f Initiator efficiency

F Mole fraction of AMPTMA-repeating units in a

copolymer

f(NMR) Mole fraction of AMPTMA in the reaction

mixture by NMR

HEMA 2-hydroxyethyl methacrylate

I* Initiating radical

11

IL Ionic liquid

IL-A 2-(1-butylimidazolium-3-yl)ethyl methacrylate

tetrafluoroborate

IL-A Br 2-(1-butylimidazolium-3-yl)ethyl methacrylate

bromide

IL-B 3-methyl-1-(4-vinylbenzyl)-1-imidazolium

chloride

kact Rate constant of activation

kadd Rate constant of addtion

KATRP Equilibrium constant of ATRP

kd Rate constant of initiator decomposition

kdeact Rate constant of deactivation

ki Rate constant of initiation

KOTf Potassium trifluoromethanesulfonate

kp Rate constant of propagation

kt Rate constant of termination

L Ligand

LAM Less activated monomer

LCST Lower critical solution temperature

LiNTf2 Lithium bis(trifluoromethane)sulfonamide

LiOTf Lithium trifluoromethanesulfonate

M Monomer

MADIX Macromolecular design by interchange of

xanthate

MALDI Matrix-assisted laser desorption/ionization time-

of-flight mass spectrometry

MAM More activated monomer

Me6TREN Tris(2-(dimethylamino)ethyl)amine

MeCN Acetonitrile

MeOH Methanol

Micro-DSC Differential scanning microcalorimetry

Mn Number average molecular weight

Mt Metal

Mw Weight average molecular weight

NaTFA Sodium trifluoroacetate

NIPAm N-isopropyl acrylamide

NMR Nuclear magnetic resonance

NTf2, Tf2N, TFSI Bis(trifluoromethane)sulfonamide

OTf Trifluoromethanesulfonate

PAMPTMA Poly((3-acrylamidopropyl) trimethylammonium

chloride)

PClMeSt Poly(p-chloromethylstyrene)

PDMAEMA Poly(2-(dimethylamino)ethyl methacrylate)

PEDOT Poly(3,4-ethylenedioxythiophene)

12

PIL-A Poly(2-(1-butylimidazolium-3-yl)ethyl

methacrylate tetrafluoroborate)

PIL-A Br Poly(2-(1-butylimidazolium-3-yl)ethyl

methacrylate bromide)

PIL-A Br-PNIPAm Poly(2-(1-butylimidazolium-3-yl)ethyl

methacrylate bromide)-block-poly(N-isopropyl

acrylamide)

PIL-A-PNIPAm Poly(2-(1-butylimidazolium-3-yl)ethyl

methacrylate tetrafluoroborate)-block-poly(N-

isopropyl acrylamide)

Pm* Polymeric radical with degree of polymerization

m

PMDETA N,N,N′,N′′,N′′-pentamethyldiethylenetriamine

PMMA Poly(methyl methacrylate)

PMOTAC Poly(2-methacryloyloxyethyl

trimethylammonium chloride)

PMOTAI Poly(2-methacryloyloxyethyl

trimethylammonium iodide)

Pn Polymer with degree of polymerization n

Pn* Polymeric radical with degree of polymerization

n

PNAGA Poly(N-acryloylglycinamide)

PNIPAm Poly(N-isopropyl acrylamide)

Pn-X A polymer with halide as an endgroup

PS Polystyrene

R* Re-initiating radical

RAFT Reversible addition-fragmentation chain transfer

Rh Hydrodynamic radius

RI Refractive index

Rp Rate of polymerization

RT Room temperature

RTIL Room temperature ionic liquid

SARA ATRP Supplemental activators and reducing agents

ATRP

SEC Size exclusion chromatography

S-I-S Soluble-insoluble-soluble

t Time

TBAB Tetrabutylammonium bromide

Tc Cloud point

TcL LCST-type Tc

TcU UCST-type Tc

Tg Glass transition temperature

THF Tetrahydrofuran

Tmax Temperature of maximum heat capacity

13

UCST Upper critical solution temperature

UV Ultraviolet

ΔH Enthalpy change of transition

ΔTcU Diffrence of TcU between heating and cooling

14

1. Introduction

Thermoresponsive polymers are combined with non-classical polyelectrolytes in this

thesis. The special focus is on polyelectrolytes that can be turned insoluble in water with

suitable counter ions, and the solution behavior of these systems. The polymers have been

synthesized with controlled radical polymerization methods. The introductory part gives a

short review of the used materials and synthesis methods.

1.1. Controlled Radical Polymerization

All the polymers in the present study are synthesized either by atom transfer radical

polymerization (ATRP) or reversible addition-fragmentation chain transfer (RAFT)

polymerization, both of which are controlled radical polymerization methods.

Both approaches insert periods of dormancy between much shorter periods of activity.1

In this way, it is possible to extend the lifetime of the propagating radical over the course

of the whole reaction. Irreversible termination is thus suppressed, but not completely

absent.2 Nevertheless, provided that the activation-deactivation cycles are frequent

enough, all the chains have nearly an equal chance of growing and thus the polydispersity

of the final product remains low. Also the polymerizations follow first order kinetics

respect to the monomer.2

Both ATRP and RAFT rely on quasi-equilibrium between the active and dormant

states. This is achieved by very different means as ATRP is based on the persistent radical

effect and RAFT on degenerative chain transfer.2 ATRP and RAFT are described in some

detail below. The controlled radical methods are not limited to ATRP and RAFT, but

include e.g. iodine-transfer polymerization3 and nitroxide mediated polymerization

(NMP)4, but these are outside the scope of this text.

1.1.1. ATRP

ATRP was discovered in 1995 independently by Wang and Matyjaszewski5 and by Kato

et al.6. The equilibrium between the active and dormant states is achieved by using metal,

usually copper, salts, which mediate equilibrium between the active and dormant species

(scheme 1).7 It is also possible to use an organic photoredox catalyst instead of a metal

salt.8-10 Mechanistically, ATRP has its roots in atom transfer radical addition (ATRA).11-14

15

Scheme 1. The ATRP equilibrium.7

In the mechanism, a reactive alkyl halide (Pn-X) reacts with a metal (Mt), complexed with

a ligand (L), which produces a reactive radical Pn* and the metal with a higher oxidation

state. The metal in the higher oxidation state acts as a persistent radical.7, 15-17 Pn-X is

initially a small molecular initiator, but after the equilibrium has been established it is the

dormant polymeric species.

After it has been formed, Pn* then propagates and adds monomers (M) with the rate

constant kp. Termination is inevitably present and dead polymer is formed with the rate

constant kt. In order to establish a good control of the polymerization, initiation should be

fast and quantitative.11 Each initiator molecule is assumed, in the absence of termination

and chain transfer, to produce exactly one polymer chain. Therefore, the theoretical degree

of polymerization (DPtheor.) is only dependent on the ratio between initial concentration of

the monomer ([M]0) and the initiator ([I]0) along with the conversion of the monomer

(conv). DPtheor. can be calculated according to equation 1.11 The [M]0/[I]0 ratio, i.e. the

theoretical degree of polymerization at full conversion, is also known as the targeted

degree of polymerization, DPT.

convDPconvI

MDP (1) T

0

0

theor.

ATRP is an (quasi-)equilibrium process so the aforementioned activation reaction also

reverses with a rate constant of kdeact.7 This reverse process reduces the metal and produces

the dormant species Pn-X. The equilibrium between the forward and reverse processes

(equilibrium constant KATRP) is the key to the control in ATRP and can be described with

equation 2, which can in turn be used to express the rate of polymerization (Rp) with

equation 3.7, 18 Henceforth, all the equations are formulated assuming copper salts, because

copper is the most widely used metal in ATRP, but they are valid for some other metals

too.7

XPCu(I)/L

Cu(II)/LX*P

k

kK (2)

n

n

deact

act

ATRP

16

Cu(II)/LX

MCu(I)/LXPKk*PMkR (3) n

ATRPpnpp

It can be observed from equations 2 and 3 that the rate of polymerization is influenced by

KATRP, which is a measure of catalyst activity. KATRP is affected by solvent polarity; it

increases with increasing polarity.19 The activity of the catalyst is mostly determined by

the ligand. With different ligands KATRP can span over 7 orders of magnitude from

approximately 10-10 to 10-3, meaning that the equilibrium is heavily on the side of the

starting materials.20 KATRP is directly related to the electrochemical properties of the

complex, with more reducing catalysts yielding higher values of KATRP.19, 20 Also, the

nature of the used halogen has an effect on KATRP.16

An ideal ligand should have a large KATRP to allow fast polymerization with a small

amount of copper, but also a large kdeact. kdeact influences the polydispersity, i.e.the ratio

between weight average (Mw) and number average (Mn) molecular weights of the

produced polymer according to equation 4.7, 20 Two classical ligands that fulfill these

requirements, tris(2-(dimethylamino)ethyl)amine (Me6TREN) and N,N,N′,N′′,N′′-

pentamethyldiethylenetriamine (PMDETA), are shown as examples in scheme 2.20

1

conv

2

Cu(II)/LXk

XPk

DP

11

M

M (4)

deact

np

n

w

Scheme 2. Two classical ATRP ligands.

Copper (II) salts are often added to the reaction mixture, since they decrease the likelihood

of early terminations as they act as persistent species and bring down the polydispersity

according to equation 4.17 This comes with the cost of lower rate of polymerization, as can

be seen from equation 3.21-24

Along with low polydispersity of the synthesized polymers, one of the largest

advantages in using ATRP is the straightforward synthesis of block copolymers. As the

majority of the chains contain a halide as their end group, they can be used as

macroinitiators in the synthesis of block copolymers.1, 5, 7 The ease of attachment of

17

ATRP-initiating groups allows also the synthesis of more complex macromolecular

architectures, such as brushes, stars, and surface grafts.1

ATRP can be conducted by reducing copper (II) to copper (I) in situ. This method is

known as activators generated by electron transfer for ATRP (AGET ATRP).25

From equation 4, it can be observed that the rate of polymerization is dependent on the

Cu(I)/Cu(II)-ratio, not the absolute concentrations of the species. This can be used as an

advantage to reduce the amount of copper by performing an AGET ATRP polymerization

with a very low amount of copper salts and an excess of reducing agent in order to

compensate the Cu(II) formed in termination reactions.26 This is known as activators

regenerated by electron transfer for ATRP (ARGET ATRP). The modification of ARGET

ATRP which uses zerovalent metals as co-activators and reducing agents is known as

supplemental activators and reducing agents ATRP (SARA ATRP).27-30

1.1.2. RAFT

Besides ATRP, the other major controlled radical polymerization method is reversible

addition-fragmentation chain transfer (RAFT), which was introduced in 1998 by Chiefari

et al.31 RAFT is based on degenerative chain transfer.32 The mechanism of RAFT is

presented in scheme 3. RAFT usually uses thiocarbonylthio-compounds as chain transfer

agents (CTAs), which are sometimes referred as RAFT agents.32

Scheme 3. The mechanism of RAFT.33

The RAFT polymerization is initiated as a traditional radical polymerization (step I in

scheme 3). Radical I* then initiates the polymerization with a rate constant ki. The most

common method of producing initiating radicals is the use of thermally decomposing

18

initiators31, 32, but other methods like ultraviolet (UV) light decomposing initiators34, γ-

radiation35, 36, or redox-initiation37 are also possible. This step introduces excess of

radicals to the system, which invariably produces terminated chains.38 This can be

circumvented by initiating the polymerization as in ATRP directly from the CTA.39-41

Polymeric radical (Pm*) that is produced by the initiator adds to the reactive double

bond between carbon and sulfur in step II.33 This reaction has a rate constant kadd and it is

reversible. The intermediate radical can fragment either back towards the polymeric

radical or liberate a re-initiating radical (R*) with the rate constant kβ. Should this happen,

a new polymer chain is created in step III.

It can be observed from steps I, II, and III in scheme 3 that the number of polymer

chains in RAFT is determined by the amount of original initiator radicals and R-groups in

the CTA. Therefore, the theoretical degree of polymerization can be expressed with

equation 5.42 In equation 5 f is the initiator efficiency, kd the rate constant of initiator

decomposition, [CTA]0 the initial concentration of CTA, t is time, and d the average

number of dead chains produced by a termination event (combination produces one chain

and disproportionation two chains).

tk

0

0

theor.de1dfCTA

convMDP (5)

The second term in the denominator, which arises from the initiator derived chains, is

often neglected.42 This is justified by the fact that a vast majority of the polymer chains are

born during step II, as one radical can potentially react to trigger the cleavage of R-groups

of many CTA-molecules. Therefore, equation 5 can be simplified to equation 6.

0

0

theor.CTA

convMDP (6)

After all of the initial CTA is consumed, the main RAFT equilibrium (step IV in scheme

3) is established.33 The rapid exchange between the active and dormant states then ensures

the chance of equal growth for all of the polymer chains. As is the case in all radical

reactions, terminations (step V) are always present. However, majority of the polymer

chains do contain the thicarbonylthio-goup in their ends, which has also been

experimentally proven.43-45 This allows the use of the polymers as macro-CTAs in

synthesis of block copolymers46-48 and also other manipulations of the end groups49, 50.

CTAs usually belong to one of four subclasses, depending on the Z-group (scheme 4):

dithioesters, trithiocarbonates, xanthates (dithiocarbonates), and dithiocarbamates.32, 33 The

special case of conducting RAFT with a xanthate CTA is sometimes referred as

macromolecular design by interchange of xanthate (MADIX).51 Dithioesters and

trithiocarbonates are suitable for controlling the polymerizations of conjugated monomers

such as styrenes and methacrylates, which are also known as more activated monomers

(MAMs).52 The non-conjugated, less activated monomers (LAMs), e.g. vinyl acetate, are

better controlled by xanthates or dithiocarbamates. The difference has decreased after the

19

introduction of the “switchable” or “universal” CTAs, which can be used for both MAMs

and LAMs.53, 54

Scheme 4. Top: General structure of a CTA. Bottom, from left to right: a dithioester, a

trithiocarbonate, a xanthate, and a dithiocarbamate.

Generally, the Z-group modifies both the rate of addition to the carbon-sulfur double bond

(kadd in scheme 3) and the stability of the intermediate radicals in steps II and IV in

scheme 3.52 The reactivity of a CTA in chain transfer is enhanced by the presence of

electron withdrawing and radical stabilizing Z-groups.55, 56 The role of the R-group is to

act as a good leaving group (kβ ≥ k-add in scheme 3) and it should be able to efficiently

reinitate polymerization.52, 57, 58 In order to achieve efficient control of polymerization with

RAFT, the CTA needs to be carefully chosen in respect to the monomer to be

polymerized.32

1.2. ILs and PILs

Ionic liquids (ILs) are salts that have a low melting point, the ones that are liquid at room

temperature are known as room temperature ionic liquids (RTILs).59-63 Commonly, ILs

consist of an unsymmetrical organic cation, e.g. imidazolium or phosphonium, and a

smaller anion.64-66 Ionic liquids are studied for many applications, including dissolution of

cellulose67-69, extractions70-74 , and use as a reaction medium75-78.

Properties of the ILs may be affected by the choice of the anion. It is possible to turn

ILs almost insoluble in water with suitable counterions, and also other properties such as

viscosity, temperature of thermal decomposition, as well as melting point are affected.79-84

Thermodynamically, the low solubility in water arises from the negative entropy of

dissolution85, which is also the case with hydrocarbons at room temperature86-91.

The properties of imidazolium-based ILs are suggested to be due to strong, directional,

and localized hydrogen bonding that introduces “defects” in the charge symmetry, in

combination with the entropic gain arising from many different conformations.92-97 The

evidence supporting the localized hydrogen bonding has been questioned and thus the

anion-cation interactions could also be purely of ionic nature.98-100 However, most studies

20

seem to agree that although coulombic forces account for the majority of interactions in

ILs, the effect of the hydrogen bonds is far from being negligible.101-103

Polymeric ionic liquids (PILs) are polymers “that feature an ionic liquid (IL) species in

each monomer repeating unit, connected through a polymeric backbone to form a

macromolecular architecture”.104 It is unclear to the author why the physical state of the

monomer is important. However, several researchers nowadays take polyelectrolytes as

ionic liquids. This has been also the author’s approach throughout this thesis and therefore

it is appropriate to discuss PILs in some detail.

The first PILs were synthesized by Ohno and Ito in 1998 and since then the field has

expanded rapidly.105-107 Commonly PILs are based on polycations, but also polyanions

that are called PILs have been reported.

Anion responsive PILs were first reported by Marcilla et al.108-113, after which many

studies on the topic have been conducted114. The same anions often bring analogous

properties for PILs as for ILs. For example, anions that cause ILs to be only sparingly

soluble in water84, 115 also yield water-insoluble PILs108, 109, 116 . In addition, the effect of

anions on the glass transition temperatures (Tgs) of PILs116-119 generally follows similar

trends as it does on the melting points of ILs80, 82, 120. In the sections below, the focus is on

anion responsive PILs.

1.2.1. NTf2 and Other Hydrophobic Anions

An especially important anion, both generally and for this work in particular, is

bis(trifluoromethane)sulfonamide (NTf2, Tf2N, TFSI) (scheme 5), which was introduced

for ILs in 1996 by Bonhôte et al.79 It turns ILs very poorly soluble in water, but water is

moderately soluble in ILs with NTf2 as counterion.84, 85, 121-124 It causes ILs to have low

melting points and may even turn them completely amorphous.80, 82, 125, 126 Analogously,

PILs with NTf2 as a counterion tend to have a low Tg for a polyelectrolyte117, 118, 127-129 and

they are insoluble in water but soluble in polar organic solvents108, 110, 130-133.

Scheme 5. Structure of NTf2 anion.

A common way of rationalizing the properties of NTf2 is its inability to form strong

hydrogen bonds.79, 134-140 Simulations indicate that the anion-cation interactions in NTf2

containing ionic liquids are mostly electrostatic and weak, a result which has also been

experimentally proven.141-143 Also, the large size of the anion and the subsequent low

charge density, has an impact on the cation-anion interactions.135, 143 Probably both the

inability to form hydrogen bonds and low polarizability of the anion contribute to the

21

NTf2-induced water insolubility.144 The thermodynamic reason to the low solubility of

organic salts of NTf2 in water is the unfavorable entropy of dissolution, which was the

case for other hydrophobic anions as well.85, 121, 145, 146

It is possible that the -CF3-groups of NTf2 are on the same side of S-N-S-bond (cisoid

form) or on the opposite sides of the bond (transoid form).147, 148 The favored

conformational isomer is dependent on the environment and cation, but both can exist in

liquid state.135, 149-154

Along with its use in ILs and PILs, the main application of NTf2 as its lithium salt

(LiNTf2) is in battery electrolytes.155-158 NTf2 is a conjugate base of a strong acid, so its

protonation should not be significant in most applications.159-161 This is due to the ability

of the anion to delocalize the negative charge.162-164

PILs can be made insoluble in water also with trifluoromethanesulfonate (OTf), known

as triflate.108, 109, 112 PILs with other fluoroanions, BF4- and PF6

-, are also insoluble in

water.109, 111, 165-168 These anions always hydrolyze to varying degrees in contact with

water and thus a system with BF4- or PF6

- in reality contains a mixture of ions, which is

especially pronounced with BF4-.70, 169-178 This is seldom discussed in the PIL literature,

including one of the publications by the author.I

1.2.2. Applications of PILs in Colloids

This section explores various applications of PILs in colloids, since they are important in

the framework of this study and are one of the most popular fields of PIL research. PILs

are also used in many other applications.104, 106, 114, 179-186

One of the first applications was the stabilization of aqueous dispersions of carbon

nanotubes and graphene, both with polyanion and polycation PILs.113, 187-196 The ability of

imidazolium-containing compounds to stabilize carbon nanomaterials can be understood

via the formation of π-π- and cation-π interactions between the imidazole ring and

graphene.113, 195-197 The adsorbed polymer then provides steric and electrostatic

stabilization. The anion-dependent solubility of polycation-PILs can be utilized to

precipitate the materials or to transfer them to an organic medium.113, 193-195

Similarly to carbon nanomaterials, PILs can be applied in stabilization of metal

nanoparticles, metal nanorods, and other nanomaterials.113, 198-202 The anion-dependent

solubility can be utilized in the case of these nanomaterials.113, 198-200

The interactions between the imidazolium ions and graphene can also be utilized in a

more macroscopic way. This was first shown by Fukushima et al., who dispersed carbon

nanotubes (CNTs) in polymerizable ILs, which yielded a gel-like material or “bucky

gel”.189, 203 The dispersion can be then polymerized in order to form PIL-CNT

composites.189, 204, 205 Use of NTf2 as an anion is advantageous in the formation of bucky

gels, since it brings down the melting point of ILs and thus allows easier formation of

dispersions. Similar approach can be used with other materials, such as cellulose, to yield

PIL composites.206-212

Interactions between polymeric imidazolium salts and conductive polymers can be

utilized in a similar fashion as with carbon nanotubes and graphene. Poly(3,4-

22

ethylenedioxythiophene) (PEDOT) combined with PILs is probably studied the most 213,

but polyaniline110 and polypyrrole110, 112 have also been reported. Stable aqueous

dispersions of conductive polymers can be formulated by either synthesizing the polymer

in the presence of a PIL110, 112, 198, 214-218 or by introducing PIL-like groups to the

conductive polymers219-221. Anion exchange causes the dispersions to precipitate, as is

common with PIL-systems.110, 112, 215-219, 222 The materials can then be dispersed in polar

organic solvents. Electrochemical polymerization directly on electrodes is also possible, as

with more traditional conductive polymers.222, 223 Hydrophobic anions increase the water

contact angle compared to traditional PEDOT-formulations.216, 217, 222, 223 This is

advantageous, since absorption of water can have a detrimental effect on the performance

of devices that use conductive polymers.224-228

In addition to the mentioned colloidal applications for PILs, colloids made from PILs

themselves are being intensely studied. 186 Several types of PIL-colloids have been

reported: micro- or nanoparticles229-237, solvent-swollen microgels111, 237-241, self-

assembled structures131, 132, 242-244, surface-grafted particles245-250, and seeded core-shell

structures251-253. These often show anion-dependent solubility.111, 132, 234-238, 243-246 Also

macroscopic PIL-gels, often anion responsive, have been synthesized.165, 241, 243, 254-258

Most of the systems described in this section use the anion exchange as a stepwise

“on/off-switch”. However, it is also possible to alter the properties of PILs continuously

with a partial anion exchange to yield a “copolymer”. Much like the classical

copolymerization 259-261, a partial anion exchange can be used to vary Tg of PILs262. Partial

anion exchange influences the self-assembly of PIL containing diblock copolymers131, 132

or even turns a PIL homopolymer to an amphiphile.244 Other properties can also be fine-

tuned by partial anion exchange.263-265

1.3. Thermoresponsive Polymers in Water

The two basic types of thermoresponsive behavior are lower critical solution temperature

(LCST) and upper critical solution temperature (UCST). Polymers that have a LCST in a

solvent display a decrease in solubility with increasing temperature and polymers with an

UCST with decreasing temperature. There are variations inside the two types and

sometimes both can even coexist in a system.266

This section describes some relevant aspects of thermoresponsive polymers in water in

the framework of the studies described in this thesis. Poly(N-isopropyl acrylamide)

(PNIPAm) (scheme 6) and the LCST-phenomenon are described in the same section. The

reason for this is that PNIPAm is by far the most studied polymer with LCST, and

therefore a major part (or even majority) of LCST-studies have been conducted with

PNIPAm.266 However, many other polymers with LCST-behavior are also known.267

23

Scheme 6. Structure of PNIPAm

1.3.1. PNIPAm and the LCST Phenomenon

The existence of LCST-type phase transition for PNIPAm was first described by Heskins

and Guillet in 1968.268 Probably the most commonly cited value for the cloud point (Tc)

for PNIPAm is 32 °C, although many factors may cause variation to the actual

temperature.269

The cause for the phase transition is that water turns from a good to a poor solvent for

PNIPAm with increasing temperature, which leads to coil-to-globule-transition.270 This is

manifested by the decrease of the second virial coefficient (A2). The formation of compact

structures can be observed as a decrease in both hydrodynamic radius and radius of

gyration.270-273

The decrease in the solvent quality leads to the destruction of the hydration layer or

“water gage” around the isopropyl groups and partial dehydration of the polymer

chains.274-278 This causes the association of the polymer, through breaking of a fraction of

the polymer-water hydrogen bonds and formation of new polymer-polymer hydrogen

bonds.276, 279-282 A vast majority of amide groups of the polymer keep hydrogen bound to

water even at temperatures above Tc and the polymer globules contain a substantial

amount of water.279, 281

Hysteresis is observed when cooling PNIPAm solution back to temperatures below the

cloud point.283 This is attributed to the newly formed intra- and intermolecular hydrogen

bonds.276, 279, 283 It can take a long time for all of the new hydrogen bonds to break,

especially if the sample is kept at high temperatures for prolonged periods of time.276, 283,

284 The redissolution has been observed to be a two-stage process, with the shells of the

formed aggregates dissolving first, followed by the dissolution of the cores.283

The transition takes place in “cooperative units”, which consist of the whole chain for

a low molar weight PNIPAm, but only parts of the chain for a larger polymer.285, 286 The

size of a cooperative unit has been reported to be between 85 and 600 repeating units.274,

287

In extremely dilute solutions, single chain globules can be observed.271-273 With higher

concentrations, colloidally stable multi chain aggregates, known as mesoglobules, form at

temperatures higher than Tc.288-290 The size of the globules is affected by possible ionic

groups from initiators291, by polymer concentration291-293, and significantly by the heating

rate292, 293. At temperatures well above Tc, PNIPAm mesoglobules may be regarded as

24

glassy spheres kinetically unable to aggregate.293-295 The aggregates carry a small negative

charge of unknown origin, even if the polymer is synthesized using a nonionic initiator.293

This charge may also contribute to stabilization of the structures. It is important to notice

that although colloidal PNIPAm above its Tc remains dispersed for a long time, it is only

metastable.296

It was pointed out already in the original publication on the LCST behavior of

PNIPAm that the transition is endothermic and therefore, in order to satisfy the condition

of a negative change of free energy, it must be entropy driven.268 It has been later

concluded that the driving force behind the phase transition is the entropy gained by the

release of structured water around the isopropyl groups to the bulk of the solution.274, 281,

283, 297-301 The relatively high enthalpy of the transition (4.2-8.0 kJ/mol of repeating units

for PNIPAm homopolymer in pure water274, 280, 297, 302-304) is mainly attributed to the

breaking of hydrogen bonds within the structured water, since it is known that hydrogen

bonding in water gages is stronger than in bulk.275, 281 It is unlikely that the difference

between the polymer-water and water-water hydrogen bonds would be as high as the

observed enthalpy change, especially because this only concerns a minority of the amide

groups.280 Thus the contribution from these changes in hydrogen bonding to transition

enthalpy is small.

Low concentrations of certain salts, like NaI and NaSCN, increase Tc of PNIPAm, but

generally the addition of salts decreases the phase transition temperature.274, 281, 303, 305 The

magnitude of the effect follows the Hofmeister series and is more related to the anion of

the salt, the cation has only a minimal effect.303 The anions with a strong impact on Tc are

known as kosmotropes, the ones with weaker impact are known as chaotropes.305 Other

additives, such as surfactants306-308 or solvents308-312, may also be used to change the phase

transition temperature.

The influence of salt on Tc is due to amide-anion interaction, polarization of first-

hydration-shell-water by the anion, and changes in surface tension around the hydrophobic

groups.305, 313-316 It is also possible that the effect is caused by interactions between the

cation of the salt and the amide oxygen, the strength of which is modulated by the

anion.317, 318 Other possible reasons have been suggested, e.g., difference in the

preferential interactions between coil and globule states for different ions319 as well as the

influence of the salt on the structure of bulk water303.

The chain topology has a major effect on the transition temperature, which is seen as

higher phase transition temperature of cyclic PNIPAm compared to its linear analogue of

similar molecular weight.320, 321 Also, a completely opposite result has been reported.322

The conflicting results are explainable by the different methods used to couple the chain

ends.323 Cyclic PNIPAm forms different mesoglobular structures than the linear one.301

Stereoregularity of PNIPAm has a large impact on the cloud point. Increasing isotactic

content of the polymer quickly decreases Tc and with higher content of meso-diads the

polymer becomes completely insoluble in water.304, 324-326 Analogously, an increase in

syndioctacticity increases Tc, but the effect is much weaker than in the case with

isotacticity.326-328

With high molecular weight PNIPAm, the cloud point varies less than 10 °C with

concentration.284, 329 The minimum of Tc, the LCST, is reached with PNIPAm weight

25

fraction of approximately 45 %. Above weight fraction of 70-80 %, Tg of the system is

higher than Tc and thus no phase separation can be observed.284, 329

For molecular weights above 50 kg/mol, Tc is independent of molecular weight.330

With lower molecular weights, the cloud point increases with decreasing chain length.299,

331, 332 The effect of the end group on the cloud point becomes significant. As can be

expected, hydrophilic end groups lead to higher and hydrophobic ones to lower values of

Tc.299, 300, 302, 326, 333-336 This effect diminishes quickly with increasing molecular weight

and therefore decreasing proportion of the end groups.299, 302, 326, 333-335 PNIPAm with

highly hydrophobic end groups that form aggregates already below Tc may break the rule

of hydrophobic end groups decreasing the transition temperature.300, 336-338 This is due to

isolation of the hydrophobic groups inside the aggregates, from where they are unable to

affect the phase transition of the dangling PNIPAm-chains.300, 336-338 In this sense,

hydrophobic blocks of PNIPAm block copolymers are also considered end groups.337-339

Copolymerization affects the cloud point in a much similar fashion as the end groups

do, though the effect is weaker with a given comonomer content than with the same

relative amount of end groups. 281, 298, 300, 340-346 The stronger effect of the end groups has

been attributed to initiation of the dehydration from the mobile end groups, which is then

followed by the phase transition of the bulk of the chain.300 As an exception, charged

comonomers increase Tc quickly.346

The enthalpy change associated with the transition of PNIPAm copolymers decreases

as a function of the transition temperature.281, 343, 347-349 The decrease is a linear function of

the cloud point, regardless of the comonomer used.281, 347 In the case of hydrophilic

comonomers, the effect has been explained by the increase of overall hydrophilicity of the

polymer, which raises the transition temperature. 281, 347, 348 Hydrogen bonding is weaker

at elevated temperatures and when the phase separation finally takes place, this is seen as

reduced enthalpy of transition. Analogously, incorporation of hydrophobic monomers,

which decreases the transition temperature, leads to higher transition enthalpies.

Alternatively, it may be that incorporation of hydrophilic comonomers causes less water to

be released during the phase transition, which leads to lower enthalpy.349

1.3.2. UCST

Far less articles are published about UCST in water than about LCST.266 Polymers with

UCST in water can be divided to two rough categories, depending on whether their UCST

is based on Coulomb interactions or hydrogen bonding.350

The polymers having a Coulomb type UCST are usually zwitterionic polymers, the

most notable class is poly(sulfobetaines).351 The polybetaines have an UCST behavior in

salt solutions. This is due to the screening of the opposite charges and it is possible to

modulate the cloud point with electrolytes.352 Tc may increase with small amounts of salt,

but generally it decreases with higher amounts, even to complete solubility. The

magnitude of the decrease follows the Hofmeister series.353, 354 Tc can also be influenced

by copolymerization.355

26

Polymers with hydrogen bonding based UCST typically contain a primary amide

group, simplest of these being poly(methacrylamide).266, 356, 357 Also other groups that

contain both hydrogen bond donor and acceptor have been used.358-360 Probably the most

studied polymer of the class is poly(N-acryloylglycinamide) (PNAGA) , which has a

cloud point of 8-28 °C in pure water, depending on the concentration.361 The molar mass

dependence of Tc for PNAGA is insignificant.362, 363

Tc of UCST polymers can be influenced by copolymerization, much like the Tc of

PNIPAm.360, 361 The presence of ionic groups decreases the Tc of PNAGA rapidly; even a

minute amount is enough to cause the transition to disappear completely in pure water.362,

364, 365

Certain hydrophilic and hydrophobic monomers can be copolymerized to yield

copolymers with an UCST-type phase transition, even when the respective homopolymers

show no transition.350 This makes it possible to fine tune the transition temperature by

varying the ratio of the monomers.357, 366-371 Also, copolymers with response to other

stimuli, such as pH, along with temperature can be conveniently made in this way.366-369

It is possible to introduce UCST-like behavior by constructing a system that contains

thermoreversible complexes. Polymer complexes with UCST-type transition based on

hydrogen bonding 372-374 and ion-dipole interactions375 have been reported. It is also

possible to induce UCST-like behavior by host-guest interactions.376-378

1.3.3. PDMAEMA and Quaternized PDMAEMA

Another polymer with LCST behavior and significance for this work is poly(2-

(dimethylamino)ethyl methacrylate) (PDMAEMA) (scheme 7A). It is a weak base, the

values of the apparent pKa of the protonated form of PDMAEMA range between 6.2 and

7.8, depending on determination conditions.379-384 A methylated derivative of PDMAEMA

is a strong polycation. It is commonly synthesized as poly(2-methacryloyloxyethyl

trimethylammonium chloride) (PMOTAC) with chloride as counterion or as poly(2-

methacryloyloxyethyl trimethylammonium iodide) (PMOTAI) with iodide as counterion

(scheme 7B).

Scheme 7. A: Structure of PDMAEMA. B: Structure of PMOTAC (X=Cl) and PMOTAI (X=I).

27

Due to its nature as a weak base, the cloud point of PDMAEMA is adjustable with pH.380,

382, 385-387 The cloud point increases as the polymer becomes more charged, i.e. pH

decreases. Above pH 9, the molecular weight of the polymer has a significant effect on

Tc.382 In less basic conditions, the charging of the polymer is the dominating factor that

determines Tc. The enthalpy of transition increases with increasing Tc386, 387 The pH-Tc

relationship is not limited to PDMAEMA; similar behavior has also been observed for

other poly(2-(dialkylamino)ethyl methacrylates).380, 388, 389

In the presence of multivalent counterions, PDMAEMA develops an UCST behavior

at values of pH in which the polymer is protonated.390, 391 The same phenomenon has been

observed for quaternized PDMAEMA392, 393 and other polycations394, 395 with multivalent

counterions. It has been shown that both protonated PDMAEMA and PMOTAC can form

water-insoluble systems with hydrophobic monovalent counterions, including NTf2.109, 396,

397

1.3.4. Thermoresponsive PILs

A few examples of PIL-homopolymers with thermosensitive behavior in aqueous solution

have been reported.398

One report has been published prior to the work described in this thesis, which

describes PILs with UCST-type behavior in water. This was done by Yoshimitsu et al.,

who studied imidazolium-derivatized vinyl ethers with various counterions.399 They found

that the polymers with BF4- show UCST, which can be influenced with addition of salts

and with different end groups. The Tc was below 40 °C in every case. ILs with UCST-like

phase transition in water are also known.400-403 The cloud points for ILs do not indicate

complete, but only partial immiscibility.400, 401

More examples of PILs with LCST-type transition exist. These are often sulfonate

group containing polyanions with a cation familiar from ILs, often tetraalkyl

phosphonium.190, 404-408 The cloud points can be varied by varying the hydrophobicity of

the cation.404, 405 The transition temperatures are highly dependent on polymer

concentration and added salts. 190, 405-407

It is also possible to observe a LCST transtition for a strong polycation based systems,

poly(trialkyl-l-4-vinylbenzylphosphoniums) or poly(trialkyl-l-4-vinylbenzylammoniums)

with alkylsulfonate anions.409, 410 Tcs of these systems are highly dependent on polymer

concentration and the addition of salts. In addition to that, LCST behavior can be induced

for polycations by temperature-sensitive host-guest interactions, much like what is also

possible for UCST-systems.411

LCST-type of phase transition can also exist for ILs. 405, 406, 409, 412 This is possible by

combining anions and cations with suitable hydrophilicity or hydrophobicity.413

28

1.3.5. PIL-PNIPAm Copolymers

A relevant, though scarcely studied, topic in the framework of this thesis are PIL-PNIPAm

copolymers.

Relatively few studies utilizing random copolymers of NIPAm and an IL-monomer

have been made.187, 346, 414, 415 The main finding has been that Tc increases with increasing

fraction of charged monomer and may disappear completely with relatively low content of

IL-monomer in a salt free solution.187 Screening the charges with salts reduces the

magnitude of the effect to be far less dramatic. Practically the same result has been

achieved by copolymers of NIPAm with other strongly charged monomers that are not

ILs.416-419

Some examples of block copolymers of NIPAM and ILs have been reported. Tauer et

al. studied block copolymer of a PIL and PNIPAm, which could form core-shell particles

either by salting out the PIL block or by heating the PNIPAm block above its Tc.420 They

later added a poly(methyl methacrylate) block to a similar PIL-PNIPAm copolymer and

found out that the hydrophobic block significantly decreases the transition temperature of

PNIPAm.421 Yuan et al. showed that PIL-PNIPAm block copolymers form core-shell

structures with either increasing temperature or ionic strength.422

If the PIL block is hydrophobic enough, PIL-PNIPAm block copolymers may form

aggregates already at room temperature, even with bromide as a counterion.423-425 Similar

systems have been synthesized by grafting preformed PIL-particles with PNIPAm425, 426,

and by crosslinking NIPAm-vinylimidazole random copolymers with dibromoalkanes427.

1.3.6. Copolymers with Soluble-Insoluble-Soluble Transitions in Water

A few studies describing copolymers that have an UCST-type Tc above a LCST-type Tc in

water have been published. This kind of a system is sometimes described to have “soluble-

insoluble-soluble” (S-I-S) transitions.428, 429 Some reports on systems with “insoluble-

soluble-insoluble” have been published, but these are not relevant in the framework of this

thesis.390, 430

There is only one S-I-S system known to the author that utilizes a copolymer of

NIPAm. Bokias et al. reported a NIPAm-acrylic acid copolymer that displays S-I-S

behavior at low pH and high ionic strength.431 A copolymer of diethyl acrylamide (DEA)

and acrylic acid displays this behavior under similar conditions, as well.432 This is natural,

since poly(diethyl acrylamide) has a rather similar phase behavior as PNIPAm.433

The S-I-S transition of the copolymers is due to the UCST-type transition of acrylic

acid under similar conditions.358 Also other systems with S-I-S that contain acidic

monomers have been reported.428, 434

A series of copolymers with S-I-S transitions was studied by Longenecker et al., who

synthesized copolymers of 2-hydroxyethyl methacrylate (HEMA).429 Homopolymers of

HEMA undergo molecular weight-dependent LCST-type phase transition with low

degrees of polymerization, but are insoluble in water with DP above 50.435 Copolymers of

HEMA with various cationic monomers had S-I-S transitions in aqueous NaCl

29

solutions.429 The thermoresponsive properties of the polymers could be varied by NaCl

concentration, copolymer composition, copolymer concentration, and addition of urea.

Block copolymers of monomers that can interact by hydrogen bonding may have S-I-S

transitions.436

30

2. Objectives of This Study

The objective of article I was to gain knowledge of the associates formed by diblock

copolymers with a water-insoluble PIL block and with an electroneutral water soluble

block in aqueous solution.

It was observed that the blocks clearly interact with each other. An attempt to further

understand these interactions and study their effect on the structures of the associates at

elevated temperatures was the objective of article II.

The testing of the idea of inducing PIL-like behavior for PDMAEMA by introducing

NTf2 to a polymer solution and further manipulation of the interactions by pH was the

objective of article III. The observation of the existence of UCST for highly charged

PDMAEMA called for deeper understanding and was studied in article IV.

The objective of the study that led to article V was to reproduce similar behavior that

was observed for PDMAEMA in article III, but by separating the ionic and thermal

responses to different repeating units. This allowed more freedom in setting the cloud

point than was possible with PDMAEMA. It was hypothesized, that S-I-S transitions

might appear at some ratio of the repeating units and concentrations of salts.

31

3. Experimental

This section only qualitatively describes the experimental methods used in the thesis. The

exact descriptions can be found from the respective publications.

3.1. Syntheses

All the polymers have been synthesized with controlled radical methods. In publications I

and II also the IL-monomers were synthesized by the author. All the polymerizations and

some of the syntheses of small molecular weight compounds were performed under

nitrogen atmosphere.

3.1.1. Block CopolymersI, II

The diblock copolymers with water-insoluble block with BF4- as counter ion were

synthesized as described in scheme 8. The monomer synthesis was adapted from the

literature with some modifications.437 First, the IL-monomer 2-(1-butylimidazolium-3-

yl)ethyl methacrylate bromide (IL-A Br) with bromide as counter ion was synthesized

with standard organic reactions. IL-A Br was then precipitated from water with NaBF4 to

yield the water-insoluble monomer 2-(1-butylimidazolium-3-yl)ethyl methacrylate

tetrafluoroborate (IL-A). The monomer was then polymerized in acetonitrile (MeCN) by

RAFT, with (4-Cyanopentanoic acid)-4-dithiobenzoate (CPA) as CTA. The

polymerization was initiated with azobis(cyanopentanoic acid) (ACPA). This polymer,

poly(2-(1-butylimidazolium-3-yl)ethyl methacrylate tetrafluoroborate) (PIL-A), was then

used as a macro-CTA in the synthesis of block copolymers with PNIPAm blocks of

varying lengths to yield poly(2-(1-butylimidazolium-3-yl)ethyl methacrylate

tetrafluoroborate)-block-poly(N-isopropyl acrylamide) (PIL-A-PNIPAm).

Also, a polymer of IL-A Br, poly(2-(1-butylimidazolium-3-yl)ethyl methacrylate

bromide) (PIL-A Br) was synthesized and used as a macro-CTA to yield a block

copolymer with PNIPAm, poly(2-(1-butylimidazolium-3-yl)ethyl methacrylate bromide)-

block-poly(N-isopropyl acrylamide) (PIL-A Br-PNIPAm).

32

Scheme 8. Synthesis of PIL-A and PIL-A-PNIPAm.I

The water soluble triblock copolymers with PNIPAm were synthesized by ATRP. Copper

chloride salts with Me6TREN as a ligand were used as a catalyst system. Difunctional

initiator, diethyl meso-2,5-dibromoadipate (DEDBrA) was used as an initiator in water-

dimetylformamide (DMF) solution to first polymerize a long PNIPAm homopolymer

(PNIPAm-1). PNIPAm-1 was then used as a macroinitiator in the synthesis of poly(3-

methyl-1-(4-vinylbenzyl)-1-imidazolium chloride)-block-poly(N-isopropyl acrylamide)-

block-poly(3-methyl-1-(4-vinylbenzyl)-1-imidazolium chloride) (Block-1 and Block-2)

with SARA ATRP, using metallic copper in a mixture of water and methanol (MeOH).

The syntheses of PNIPAm and the two block copolymers are illustrated in scheme 9.

Also shown in scheme 9 is the synthesis of IL-monomer 3-methyl-1-(4-vinylbenzyl)-1-

imidazolium chloride (IL-B), which was used in the synthesis of the block copolymers. It

was synthesized by the reaction between p-chloromethylstyrene (ClMeSt) and methyl

imidazole. This monomer was also homopolymerized by SARA ATRP with the same

33

initiatior, DEDBrA, to yield poly(3-methyl-1-(4-vinylbenzyl)-1-imidazolium chloride)

(PIL-B-1).

Scheme 9. Synthesis of PNIPAm-1, Block-1, and Block-2. X=Cl or Br. PIL-B-1 and the two block

copolymers contain the same initiator fragment in the middle as PNIPAm-1, but these have been

omitted for clarity. II

3.1.2. Cationic HomopolymersIII, IV

A batch of PMOTAI (PMOTAI-1) and a second batch of PIL-B (PIL-B-2) for article IV

were synthesized by post-polymerization modification of PDMAEMA-2 with

iodomethane and poly(p-chloromethylstyrene) (PClMeSt) with methyl imidazole,

respectively. CPA was used as a CTA for PDMAEMA-2 and the reaction with

iodomethane was conducted with a method adapted from Plamper et al.393 ClMeSt was

polymerized to PClMeSt-1 using 2-cyano-2-propyldodecyl trithiocarbonate (CPDTC) as a

CTA. The polymer used in the post-modification (PClMeSt-2) was obtained by removing

34

the hydrophobic end groups with an excess of azobis(isobutyronitrile) (AIBN), according

to the method of Perrier et al.50 AIBN was used to initiate both polymerizations.

PDMAEMA-1 for article III was synthesized similarly as PDMAEMA-2, but with

ACPA as an initiator and with reaction temperature 100 °C.

The synthetic routes for the polymers for article IV are drawn in scheme 10 along with

the two counter ions that were used in the study of their solutions properties (see

discussion below).

Scheme 10. Structure and synthesis of PMOTAI-1 and PIL-B-2. Also structures of the counter ions

NTf2 and OTF are shown. PDMAEMA-1 was synthesized similarly as PDMAEMA-2, but with

ACPA as initiator and reaction temperature 100 °C.

3.1.3. Cationic Copolymers of NIPAmV

Also copolymers of NIPAm and cationic (3-acrylamidopropyl) trimethylammonium

chloride (AMPTMA) were synthesized (scheme 11). The polymerizations were initiated

with ethyl 2-chloropropionate (EClPr). Varying ratios of the monomers were used for the

copolymers (CPs), but the monomer/initiator ratio was kept at 100. With poly((3-

acrylamidopropyl) trimethylammonium chloride) (PAMPTMA-1) the ratio was 50, due to

the high molecular weight of the monomer. PNIPAm-2 was synthesized similarly to the

CPs, but no CuCl2 was used.

35

Scheme 11. Synthesis of the CPs. For PNIPAm-2 y=0 and x=0. For PAMPTMA-1 z=0 and x=1.

3.2. Characterization of the Polymers

The structures of the polymers were confirmed by 1H nuclear magnetic resonance

spectroscopy (1H NMR). NMR was used also to determine the ratios of comonomers in

both blockI,II and random copolymersV. In some occasions NMR was used to calculate the

degrees of polymerization by end group analysis.I,III,V The NMR-instruments that were

used in this study were a 200 MHz Varian Gemini 2000, a 300 MHz Varian Unity

INOVA, and a 500 MHz Bruker Avance III 500.

Two systems were used for size exclusion chromatography (SEC). The first system,

which was used in the majority of cases, consisted of a Waters 515 HPLC-pump, Waters

Styragel columns and a Waters 2410 refractive index (RI)-detector. The eluent was either

tetrahydrofuran (THF), THF with 1 % of tetrabutylammonium bromide (TBAB), or DMF

containing 1 % of LiBr. The system was calibrated either with poly(methyl methacrylate)

(PMMA) standards or polystyrene (PS) standards.

The second system consisted of a Waters 515 HPLC-pump, Waters Ultrahydrogel

columns and Waters 2410 RI detector. The samples were run in 0.8 M aqueous NaNO3

with 3 % of acetonitrile. The system was calibrated with poly(ethylene oxide) standards.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI)

was conducted using a Bruker MicroFlex instrument. Solutions of the sample, the matrix,

and the cationizing agent were mixed. A small amount of the mixed solution was injected

on the sample plate and allowed to dry. Either 2,5- dihydroxy benzoic acid (DHB) or

trans-3-indoleacrylic acid (IAA) were used as the matrix. The cationizing agent was NaBr,

NaBF4, or sodium trifluoroacetate (NaTFA).

36

3.3 Solution Properties

3.3.1. Sample Preparation

The samples for transmittance measurements of PDMAEMA-1, PMOTAI-1, PIL-B-2,

PAMPTMA-1, PNIPAm-2, and the CPs were made by first mixing all other additives and

then adding the polymer as a 10 mg/mL stock solution with vigorous stirring.III-V The

PDAMEMA-1 solutions were buffered, unless otherwise noted. Similarly made samples

were also used for differential scanning microcalorimetry (micro-DSC).III,V

Stock solutions with concentration of 1 mg/mL of PNIPAm-1, Block-1, and Block-2

were directly dissolved in water and stored in a fridge.II The other samples were diluted

from these solutions. The stock solutions were used in micro-DSC and zeta potential

measurements.

Micelles of PIL-A-PNIPAm-block copolymers were made by solvent exchange from

DMF to water by dialysis. The concentrations of the micelles were determined

gravimetrically.

3.3.2. Transmittance MeasurementsII-V

Transmittance as a function of temperature was measured with a JASCO J-815 CD

spectrometer equipped with a PTC-423S/15 Peltier-type temperature control system. The

transmittances of the samples were monitored at wavelength 600 nm. The samples were

heated or cooled with rate of 1 °C/min and the samples were stabilized at the starting

temperature for either 30 minutes II, III, IV or 10 minutesV. The cloud points were defined as

the intersection of two tangents as illustrated in figure 1. Unless otherwise noted, the

transition temperature was always determined by approaching from the soluble side, i.e.

LCST-type Tc (TcL) from a heating curve and UCST-type Tc (TcU) from a cooling curve.

All samples were degassed in vacuum prior to measurements.

37

40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70

20

40

60

80

100

TcU

Tra

nsm

itta

nce

(%

)

T (°C)

TcL

Figure 1. Illustration of determination of cloud points.

3.3.3. CalorimetryI-III, V

Micro-DSC measurements were conducted with MicroCal VP-DSC microcalorimeter. The

concentration was always 1 mg/mL for polymer solutions. The PIL-A-PNIPAm-micelles

were measured as prepared. Micro-DSC was used to determine the temperature of

maximum heat capacity (Tmax) and the enthalpy change of the transition (ΔH) as illustrated

in figure 2. The samples were degassed before measurements. The values for enthalpies

and heat capacities are reported per mole of thermoresponsive repeating units. The heating

rate was 1 °C/min.

38

30 32 34 36 38 40 42 44 46 48 50

0

200

400

600

800

1000

1200

1400

1600

1800

C

p (

J/m

ol°

C)

T (°C)

Tmax

H

Figure 2. Illustration of definition of Tmax and ΔH.

3.3.4. Dynamic Light ScatteringI-III

Dynamic light scattering (DLS) was measured with Brookhaven Instruments BI-200SM

goniometer, a BI-9000AT digital correlator and a Coherent Sapphire laser 488-100 CDRH

operating at the wavelength of 488 nm. Temperature was controlled with a Lauda RC 6

CP thermostat. The scattering angle was 90 °, unless otherwise noted.

The micellar solutions were allowed to equilibrate for 5 minutes at each temperature.I

The solutions of Block-1 and Block-2 were kept in an oven at 50 °C overnight.II All of the

samples of a given block copolymer were put to the oven at the same time.

All the light scattering samples were membrane-filtered to cleaned cuvettes.

3.3.5. Zeta potentialI, II

Zeta potentials were measured with Malvern Instruments ZetaSizer Nano-ZS equipped

with a 4 mW He.Ne laser operating at wavelength 633 nm. The temperature was changed

stepwise and the samples were equilibrated for 10 minutes at each temperature before

measurements. In some cases, also the hydrodynamic radii of the particles were measured

in the same time.

39

3.3.6. Cryo-EMI

Electron cryomicroscopy (cryo-EM) was performed with a FEI Tecnai F20 microscope

operated at 200 kV. The images were recorded with a Gatan US4000 CCD camera at a

magnification of 68,000×. The samples were vitrified with liquid ethane and a Gatan 626

cryo-holder maintained at -180 °C was used.

40

4. Results and Discussion

This section discusses the key aspects of the results. All the figures and tables have been

marked with the number of the article where the data was originally published.

4.1. Syntheses

The basic molecular properties of the synthesized polymer are presented in this

subsection. More discussion about the syntheses of the polymers is given in the articles.

Examples of NMR spectra, MALDI spectra, and SEC chromatograms are shown in the

publications.

4.1.1. Block CopolymersI, II

After its successful synthesis, IL-A was polymerized to PIL-A. The polymerization

proceeded with first order kinetics. The degree of polymerization for this polymer was

found to be 24 by end group analysis by NMR. PIL-A was then used as a macro-CTA in

the syntheses of four diblock copolymers with PNIPAm blocks of varying lengths. The

lengths of the PNIPAm blocks were calculated from the NMR spectra, taking into account

the length of the PIL-A block. Similar methodology was used to synthesize also the PIL-A

Br polymer, which was used as a macro-CTA in the synthesis of one block copolymer.

The characteristics of the polymers are summarized in table 1. The subscripts in the names

of the polymers denote the block lengths, e.g. PIL-A24-PNIPAm59 contains a PIL-A block

with DP 24 and a PNIPAm block with DP 59.

Table 1. Macro-CTAs and diblock copolymers by RAFT.I

Polymer CTA Mn

(MALDI)(kg/mol)

Mw/Mn

(MALDI)

Mn

(NMR)(kg/mol)

PIL-A24 CPA 5.5 1.1 8 .0

PIL-A24-PNIPAm14 PIL-A24 8.1 1.09 9 .6

PIL-A24-PNIPAm26 PIL-A24 9.1 1.13 11.0

PIL-A24-PNIPAm59 PIL-A24 18.3 1.03 14.7

PIL-A24-PNIPAm88 PIL-A24 26.2 1.07 18.0

PIL-A43 Br CPA 26.8 1.09 13.9

PIL-A43Br-PNIPAm105 PIL-A43-Br 38.6 1.08 25.8

The triblock copolymers were synthesized using PNIPAm-1 as a difunctional

macroinitiator. The lengths of the blocks were measured by calculating the DP of

PNIPAm-1 from SEC to be 542 and then using NMR to determine the block lengths.

41

Limited success was met in the attempt to measure the molecular weights of the block

copolymers by SEC. Although the counter ion was changed in situ to NTf2, which is

known to improve the organosolubility of polycations in general109, the measured

molecular weights are obviously too small. The distributions are narrow, however. The

molecular properties of the PNIPAm-1, Block-1, Block-2, as well as PIL-B-1, which was

synthesized for comparison, are listed in table 2.

Table 2. Difunctional macroinitiators and triblock copolymers by ATRP.II

Polymer DP(PIL) Mn (kg/mol) Mw/Mnc Mn(tot.)d(kg/mol)

PNIPAm-1 - 61.3c 1.17c 61.3

Block-1 25a 59.0c 1.16c 73.1

Block -2 44a 57.1c 1.18c 81.9

PIL-B-1 112b 26.6b 1.03 b 26.6

a. From NMR. b. From MALDI. c. From SEC in DMF with 1 % of LiBr, PMMA-standards. d. Total Mn,

taking into account all blocks, using the DP from NMR of the PIL-blocks.

4.1.2. Cationic HomopolymersIII, IV

Two batches of PDMAEMA were synthesized with the same CTA, but with different

initiators and reaction temperatures (see experimental). The molecular weight of

PDMAEMA-2 is slightly higher and the distribution is narrower. Also PClMeSt-1 was

synthesized and the end group was modified to yield PClMeSt-2. PClMeSt-2 and

PDMAEMA-2 were used to synthesize the strong polycations, PMOTAI-1 and PIL-B-2,

both modifications proceeding in a quantitative fashion. The molecular weights of the

polymers are listed in table 3.

Table 3. Characteristics of the Homopolycations.III, IV

Polymer Mn (kg/mol) Mw/Mn

PDMAEMA-1 24.1a 1.34a

PDMAEMA-2 27.4a 1.07a

PMOTAI-1 51.9c -

PClMeSt-1 15.4b 1.24b

PClMeSt-2 16.4b 1.32b

PIL-B-2 25.1c -

a. Determined with SEC in THF with 1 % of TBAB, PMMA standards. b. Determined with SEC in THF, PS

standards. c. Calculated from the precursor polymer.

42

4.1.3. Cationic Copolymers of NIPAmV

The CPs were synthesized by copolymerization of NIPAm and AMPTMA in various

ratios. The mole fraction of AMPTMA in the reaction mixture (f(NMR)) was determined

by NMR. The mole fraction of AMPTMA-repeating units in the final copolymer (F) and

f(NMR) are in a good agreement. The molecular weights obtained by different methods

vary, but it can be concluded that all the polymers are of similar size and the distributions

are narrow. The CPs have been named after their AMPTMA-content, e.g. CP-17 contains

17 mol-% of AMPTMA. The characteristics of the copolymers are summarized in table 4.

Table 4. Cationic Copolymers of PNIPAm and the Corresponding Homopolymers.V

Polymer f(NMR)a

(%)

Fb

(%)

Mn (SEC, DMF)c

(kg/mol) (Mw/Mn)

Mn (SEC,aq)d

(kg/mol) (Mw/Mn)

Mn (NMR)e

(kg/mol)

PAMPTMA-1 100 100 insoluble 2.92 (1.12) 8.93

PNIPAm-2 0 0 17.5 (1.28) 1.36 (1.07) 7.94

CP-8 8.05 7.82 24.9 (1.18) 5.90 (1.28) 11.0

CP-17 18.1 17.1 28.0 (1.21) 10.4 (1.32) 11.3

CP-26 28.1 26.4 23.6 (1.18) 9.13 (1.31) 12.2

CP-46 49.5 46.2 18.0 (1.16) 10.0 (1.26) 12.5

CP-65 68.7 65.3 insoluble 9.59 (1.19) 13.6

a. Mole fraction of AMPTMA in the reaction mixture by NMR b. Mole fraction of AMPTMA in the

copolymer by NMR. c. Measured in DMF with 1 % of LiBr after ion exchange with NTf2. Calibrated with

PMMA standards. d. Measured in 0.8 M aqueous NaNO3. Calibrated with poly(ethylene oxide) standards. e.

From NMR-spectra using end-group analysis.

In the syntheses of the CPs, the conversion of the reaction was always above 85 %.

Because of the high conversion, the agreement between f(NMR) and F does not indicate

the formation of a random copolymer. However, while optimizing the reaction conditions,

it was found out that regardless of the ratios of the comonomers or conversions, f(NMR)

and F are always similar. This indicates that the polymerizations are random, which is

important since it is known that the chain microstructure can have a large impact on the

thermosresponsive properties of copolymers.345, 371, 438

4.1.4. Naming of the Polymers

In order to increase the readability of this thesis, the names of the studied polymers are

different from those used in the articles. To reduce the confusion of the reader, the names

of the products in the thesis and the corresponding names in the articles are given in table

5. The reader can use the table as a reference for the location of the synthetic details of

each polymer.

43

Table 5. Summary of the synthesized polymers.

Name in the thesis Article Name in the article

PIL-A24 I PIL24

PIL-A24-PNIPAm14 I PIL24-PNIPAM14

PIL-A24-PNIPAm26 I PIL24-PNIPAM26

PIL-A24-PNIPAm59 I PIL24-PNIPAM59

PIL24-PNIPAm88 I PIL24-PNIPAM88

PIL-A43 Br I PIL43- Br

PIL-A43 Br-PNIPAm105 I PIL43- Br -PNIPAM105

PNIPAm-1 II PNIPAm-1

Block-1 II Block-1

Block -2 II Block -2

PIL-B-1 II PIL-1

PDMAEMA-1 III PDMAEMA

PDMAEMA-2 IV PDMAEMA

PMOTAI-1 IV PMOTAI

PClMeSt-1 IV PClMeSt 1

PClMeSt-2 IV PClMeSt 2

PIL-B-2 IV PIL-1

PAMPTMA-1 V PAMPTMA-1

PNIPAm-2 V PNIPAm-1

CP-8 V CP-8

CP-17 V CP-17

CP-26 V CP-26

CP-46 V CP-46

CP-65 V CP-65

4.2. Solution Properties of the PNIPAm and Its Block CopolymersI

,II, V

It is worth emphasizing that the PIL-block in Block-1 and Block-2 is water soluble, but in

the case of PIL-A-PNIPAm-block copolymers, the PIL macro-CTA is not. Also, two

batches of PNIPAm homopolymers were synthesized and characterized.

4.2.1. Enthalpy of Transition in Pure WaterI ,II, V

As the phase transition of PNIPAm has been the most studied topic in this thesis, it is

appropriate to show examples of that first (figure 3). The effect of the more hydrophilic

initiator fragments and lower molecular weight of PNIPAm-2 can be seen as higher phase

44

transition temperature and lower ΔH. All the micro-DSC results for the PNIPAm and

block copolymer solutions in pure water are summarized in table 6.

28 30 32 34 36 38 40 42 44 46 48 50

0

1000

2000

3000

4000

C

p (

J/m

ol°

C)

T (°C)

Figure 3. Micro-DSC-curves for PNIPAm-1 (solid) and PNIPAm-2 (dashed).II, V

The block copolymer micelles show phase transition temperatures and enthalpies that are

dependent on DP of the PNIPAm block (figure 4 and table 6).

Table 6. Micro-DSC results for PNIPAm homopolymer and block copolymers

Polymer Tmax (°C) ΔH (kJ/mol)a Article

PNIPAm-1 34.9 6.4 II

PNIPAm-2 37.4 6.0 V

PIL-A24-PNIPAm59-micelles 39.9 0.50 I

PIL24-PNIPAm88-micelles 36.4 1.0 I

Block-1 34.6 4.6 II

Block-2 34.6 5.2 II

Mix-1 34.6 5.2 II

Mix-2 34.7 5.2 II

a. Normalized to NIPAm repeating units.

45

20 30 40 50 60 70 80

0

50

100

150

200

250

C

p(J

/mo

l°C

)

T(°C)

Figure 4. Micro-DSC curves for micelles of PIL24-PNIPAm59 (solid) and PIL24-PNIPAm88

(dashed).I

The two block copolymers with lowest DP of PNIPAm-block, PIL-A24-PNIPAm14 and

PIL-A24-PNIPAm26, did not show phase transition of any kind. This, together with the

strong DP-dependency of the transition, implies that there is a part of the PNIPAm chain

in all of the block copolymers, the length of this part is higher than 26, but lower than 59,

which is not able to undergo phase transition. This may be due to crowding near the

particle surface, so that there is no room for the chain to collapse.

More probably, the phase transition is not observed due to the interaction between the

NIPAm repeating units and the PIL-units. It has been shown that ILs with BF4- as counter

ion decrease the TcL of PNIPAm in water due to weakening of the hydrogen bonds

between PNIPAm and water.439-441 The effect is mostly caused by the anion.441, 442 At high

concentrations, the IL saturates all the hydrogen bonding sites of PNIPAm and causes the

LCST behavior to disappear. The local concentration of IL repeating units, and therefore

the concentration of BF4- anions in the block copolymer micelles near the surface is high,

and thus the first NIPAm units might not be hydrated at all. The low enthalpies of the

transition for the micelles indicate that even for the part of the chain that can undergo

phase transition, the amount of hydrogen bonds to water is reduced.

The triblock copolymers Block-1 and Block-2 which contain water soluble PIL-B-

blocks also show a decrease in the enthalpy of transition compared to the macroinitiator

used in their synthesis, PNIPAm-1 (figure 5 and table 6). This indicates interactions

between the blocks. The decrease is higher for Block-1, although the PIL-B-block in the

copolymer is shorter, which is probably due to different kind of aggregates formed at the

collapsed state (see discussion below).

46

30 32 34 36 38 40 42 44

0

1000

2000

3000

4000

5000

C

p(J

/mol°

C)

T(°C)

Figure 5. Micro-DSC curves for PNIPAm-1 (black), Block-1 (red) and Block-2 (blue).II

The existence of interactions was also confirmed in two physical mixtures of PNIPAm-1

and PIL-B-1, Mix-1 and Mix-2, which have the same ratios of repeating units as Block-1

and Block-2, respectively. In this case, the interactions seem to saturate already with small

amounts of PIL-B-1, since both mixtures gave the same enthalpy change of transition

(table 6). Nevertheless, this confirms that interactions between the repeating units exist.

4.2.2. Block Copolymer AggregatesI, II

The micelles of PIL-A24-PNIPAm59 and PIL-A24-PNIPAm88, show PNIPAm-like

thermoresponsive behavior in light scattering measurements (figure 6). The transition

temperatures obtained from light scattering are in a good agreement with the values

obtained from the micro-DSC experiments. No phase transition could be observed for

micelles of the two shorter block copolymers, which is in line with micro-DSC results.

47

20 30 40 50 60

0

50

100

150

200

Rh(n

m)

T (°C)

I (a

.u.)

Figure 6. Hydrodynamic radii (Rh) (filled symbols) and intensity of scattered light (empty

symbols) as a function of temperature for PIL-A24-PNIPAm59 (■) and PIL-A24-PNIPAm88 (●).I

Also Block-1 and Block-2 have PNIPAm-like behavior (figure 7). They evidently first

form loose aggregates, since the sizes go through a high maximum before settling to a

constant value, close to that of PNIPAm-1. The formation of loose aggregates is most

probably due to electrostatic repulsions since the phenomenon is much more pronounced

for Block-2, which has a longer PIL-B-block.

Surprisingly, also the homopolymer PIL-A24 can form stable particles in water,

although the polymer itself is not soluble in water. The particles retain their size over the

studied temperature range and they are electrostatically stabilized with highly positive zeta

potentials (figure 8).

The stability of the PIL-A24 particles is explainable by contributions of two different

effects, which both make the surface to have different counter ions than the bulk of the

particle. The fact that even very small, few millimolar, concentration of NaBF4 is enough

to precipitate the particles from water supports this explanation. This cannot be due to

electrostatic screening, since the increase in ionic strength is negligible.

48

20 25 30 35 40 45 50

0

50

100

150

200

250

300R

h(n

m)

T(°C)

Figure 7. Rh as a function of temperature for PNIPAm-1 (■), Block-1 (●) and Block-2 (▲).

Polymer concentrations were 1 mg/mL.II

10 20 30 40 50 60 70

0

20

40

60

80

100

Rh (

nm

)

T (°C)

0

10

20

30

40

50

60-p

ote

ntial (m

V)

Figure 8. Hydrodynamic radius (■) and zeta potential (●) as a function of temperature for PIL-

A24-particles in water. I

49

The first effect arises from the instability of BF4- anions which produce hydrophilic

fluoride anions. This process invariably happens when BF4- comes into contact with

water.169, 170, 175, 178 It has been shown that PIL-systems with hydrophilic anions partially

exchanged to hydrophobic ones are able to self-assemble to stable particles in water, even

by direct mixing.244 The careful solvent exchange probably leads to enrichment of the

fluoride anions on the surface.

The second contributing factor probably is the partial ion exchange of the BF4- to

HCO3- which is produced from dissolved carbon dioxide. The exchange happens on the

particle surface. Similar effect has been observed to stabilize emulsion-polymerized

particles of PMOTAC with NTf2 as a counter ion.233

The zeta potentials of PIL-A24-PNIPAm59 and PIL-A24-PNIPAm88 micelles increase

suddenly with increasing temperature (figure 9). This increase is due to the phase

transition of the block copolymers, as it begins at the temperature where the scattering

intensity starts to increase. This can be rationalized by the PNIPAm moving inside the

aggregates and PIL-A-blocks getting more exposed.

20 30 40 50 60

0

10

20

30

40

50

60

70

80

90

-p

ote

ntia

l (m

V)

T (°C)

I (a

.u.)

Figure 9. Zeta potential (filled symbols) and intensity of scattered light (empty symbols) as a

function of temperature for PIL-A24-PNIPAm59 (■) and PIL-A24-PNIPAm88 (●).I

Also the zeta potentials of Block-1 and Block-2 increase during the phase transition

(figure 10). This is due to the hydrophilic PIL-B-blocks forming a shell around the

aggregated PNIPAm at elevated temperatures. Practically identical behavior has been

observed for diblock copolymers of PNIPAm and PAMPTMA.443 The negative zeta

potential of PNIPAm might be due to the absorption of OH- -ions444-450 or traces of

carboxylic acid impurities451, 452, which are the proposed reasons for the negative charge of

50

hydrophobic surfaces in water. Either way, the negative charge may contribute to the

interactions between PNIPAm and the cationic PIL-B-blocks and PIL-B-1–homopolymer,

which were observed by micro-DSC.

20 25 30 35 40 45 50

-40

-20

0

20

40

60

-p

ote

ntial (m

V)

T (°C)

Figure 10. Zeta potential as a function of temperature for PNIPAm-1 (■), Block-1 (●) and Block-2

(▲).II

It was possible to image the PIL-A24-PNIPAm59-micelles directly by cryo-EM (figure 11).

The sample contained multiple practically identical aggregates. The aggregates are larger

than could be expected from light scattering results (figure 6). 15 mM of NaBF4 needed to

be added to the samples for the imaging and this may have affected the structures.

Figure 11 shows complex aggregates that consist of multiple smaller micelles.

Amphiphilic polymers with hydrophobic side chains have been observed to form similar

bicontinuous spherical aggregates in water.453-455 The PIL-A-24-PNIPAm59 is an analogous

case, with the hydrophobic side chains emerging from the IL-A-units.

51

Figure 11. Cryogenic electron micrographs of two different PIL-A24-PNIPAm59 micelles from the

same sample in aqueous 15 mM NaBF4. The scale bar seen in bottom-left corner is 100 nm in both

cases.I

PIL-A-PNIPAm-micelles were made by solvent exchange from DMF to water. It has been

shown that similar aggregates of an amphiphilic diblock copolymer as in figure 11 may or

may not form depending on the quality of the original solvent for the blocks.456 It is

therefore possible that the structure of the aggregates may be a product of using DMF as

the original solvent and other solvents would produce other morphologies.

Based on light scattering results, under high dilution at 50 °C (figure 12) Block-1 and

Block-2 may form structures somewhat similar to those described in figure 11. The main

difference is that Block-2 aggregates are smaller and spherical whereas Block-1 forms

aggregates that consist of smaller globules connected to each other. The aggregates were

formed by heating the solutions fast, so it is improbable that they are equilibrium

structures.

The difference in the structures of the aggregates may be due to the different lengths of

the PIL-B-blocks of the triblock copolymers. Block-1 does not have a PIL-B-block long

enough to glue the smaller spheres to a big one and stabilize it. The formation of different

types of aggregates at temperatures above TcL may very well be the cause for the different

enthalpy changes of phase transition observed in micro-DSC (table 6).

Another contribution to the difference in the aggregation behavior may arise from the

different macomolecular architectures of the two block copolymers. This may have an

impact on the structure of the aggregates.457, 458 It was observed that both IL-A and IL-B

form insoluble material that can be swollen with solvents during storage. This material is

most likely due to exchange of substituents between the imidazolium rings known as

“alkyl scrambling”.166, 168, 459-461 A small amount of a monomer with two polymerizable

groups causes branching during controlled radical polymerization.462-464 Alternatively,

polymers with more than one PNIPAm-block may form.

52

0

100

200

0 10 20 30 40

P-1

(q)

(qRg)2

hard sphere

Guinier(spherical)

coil

rod

c (mg/mL)

●

0.00200.00250.0030

Rh0° (nm)127145205

Rg (nm)103127191

Rg / Rh0°

0.810.870.93

A.

1

1,5

2

2,5

0 1 2 3

P-1

(q)

(qRg)2

hard sphere

Guinier(spherical)

coil

rod

c (mg/mL)Δ○

0.00300.00350.0077

Rh0° (nm)595766

Rg (nm)464351

Rg / Rh0°

0.780.760.77

B.

Figure 12. Angular dependence of the LS intensity and corresponding dimensions of aggregates

formed by Block-1 (A) and Block-2 (B) in aqueous salt-free solutions at 50 ºC. p-1(q) is an inverse

intensity of scattered light normalized by its value extrapolated to zero angle, i.e. R(q=0)/R(q).II

4.3. Counterion-Induced UCST in WaterIII-V

While studying the effect of NTf2 on TcL of PDMAEMA-1 it was observed that the

polymer develops an UCST-type transition with a sufficient concentration of LiNTf2 when

the solutions are buffered to pH 6 (figure 13). TcU was not observed at any pH, if the pH

was simply adjusted with an acid or a base. It has been reported that PDMAEMA with

multivalent counterions can undergo an UCST type transition in a buffered, but not in an

unbuffered solution.390.

The polymer is more than half protonated at pH 6, since the apparent pKa of the

conjugate acid of PDMAEMA-1 was observed to be 6.1 in a 1 mg/mL solution in pure

water, which is in a good agreement with the value 6.2 obtained by Plamper et al. under

similar conditions.382 In reality the degree of pronation in the buffer is higher than it

seems, since the pKa of the conjugate acid of PDMAEMA has been shown to increase

with ionic strength.384

53

The phenomenon shown in figure 13 led to the finding that it is possible to induce an

UCST for polycations with anions that commonly turn ILs and PILs insoluble in water.

The fact that the UCST-type phase transtiton is possible only in buffered solutions is due

to the ionic strength of the buffer, not the buffer capacity. Based on these observations it

can be understood that a certain amount of salt is needed to trigger the UCST behavior.

10 20 30 40 50 60 70 80 90

0

10

20

30

40

50

60

70

80

90

100

Tra

nsm

itta

nce

(%

)

T (°C)

30 % (1.91 mM)

40 % (2.54 mM)

50 % (3.18 mM)60 % (3.82 mM)

70 %

(4.45 mM)

Figure 13. Transmittance as a function of temperature upon cooling 1 mg/mL solutions of

PDMAEMA buffered to pH 6, with various amounts of LiNTf2. The relative amounts of LiNTf2

given as mol-% relative to DMAEMA units. The absolute concentrations are given in

parentheses.III

4.3.1. Effect of NTf2 on TcUIV, V

The possibility to induce an UCST with counter ions was mainly studied using NTf2.

Initial testing with PMOTAI-1 and PIL-B-2 confirmed that a sufficient ionic strength is

needed for the existence of the UCST-transition for polycations. NaCl was used for this

purpose. With LiNTf2 as the only added salt, stable colloids formed. NaCl is needed to

screen the charges so that the polycation and NTf2 cannot anymore “sense” each other and

thus, the dissociation of the ion pairs is possible. Charge screening is also required in order

to allow the polymers to form globules.

TcU decreases with increasing concentration of NaCl when the amount of LiNTf2 is

kept constant (figure 14). At higher NaCl concentrations TcU reaches a plateau, with the

exact value of the TcU depending on the concentration of LiNTf2 in the solution. The

affinity of NTf2 to the polycation is high; even when the NaCl concentration is 1000-fold

to that of LiNTf2, TcU can still be observed.

54

0 200 400 600 800 1000

20

30

40

50

60

70

80

90 40 % (1.70 mM)

30 % (1.28 mM)

20 % (0.852 mM)

20 % (0.669 mM)30 % (1.00 mM)

40 % (1.33 mM)

50 % (1.67 mM)TcU(°

C)

[NaCl] (mM)

60 % (2.01 mM)

Figure 14. TcU as a function of NaCl-concentration for 1 mg/mL solutions of PMOTAI-1 (filled

symbols, solid lines) and PIL-B-2 (empty symbols, dashed lines) with 20 % (■), with 30 % (●), 40

% (▲), 50 % (▼), and with 60 % (♦) of LiNTf2 relative to the concentration of repeating units.

The absolute concentrations are given in parentheses next to each curve in black for PMOTAI-1

and in red for PIL-B-2.IV

The decrease of TcU with increasing NaCl concentration is due to the competition between

NTf2 and chloride ion on the binding to the polycation. The equilibrium is reached at high

NaCl concentrations. Alternatively, it is possible that the screening of the charges is

complete at approximately 500 mM NaCl. The possibility to influence the TcU with NaCl

makes this system flexible.

The main factor that determines the TcU of PMOTAI-1 is the absolute concentration

LiNTf2, not the relative amount to the polymer repeating units, although this also has an

effect.

As can be seen from figure 14, PIL-B-2 with LiNTf2 behaves qualitatively similarly to

PMOTAI-1, but with higher TcU in a given concentration of LiNTf2. This is because PIL-

B is more hydrophobic than PMOTAI. Also samples with 10 % relative LiNTf2

concentration was measured, but TcU was never observed. Thus when TcU for PIL-B-2 first

appears, it is already relatively high.

TcU can be induced also for PAMPTMA-1 with LiNTf2 and the value can be

modulated with the concentration of NaCl in a similar fashion as was the case with

PMOTAI-1 (figure 15). It is noteworthy that the concentrations of LiNTf2 needed to

induce TcU for PAMPTMA-1 are several times of that needed for PMOTAI-1. This is due

to the presence of the hydrophilic amide group in PAMPTMA, while PMOTAI is a less

hydrophilic ester.

55

An interesting feature seen in figure 15 is that TcU of CP-65, which has a behavior very

similar to PAMPTMA-1, is usually slightly lower compared to PAMPTMA-1. This

means that the NIPAm units in CP-65 are more hydrophilic at elevated temperatures than

AMPTMA units in the presence of NTf2-ions.

0 2 4 6 8 10 12 14 16 18 20 22

10

20

30

40

50

60

70

80

90

TcU (

°C)

[LiNTf2] (mM)

Figure 15. TcU of 1 mg/mL solutions of PAMPTMA-1 (filled symbols, solid lines) and CP-65

(empty symbols, dashed lines) as a function of LiNTf2-concentration with NaCl-concentrations of

100 mM (●), 250 mM (▲), 500 mM (▼) and 750 mM (♦). Data for PMOTAI-1 (half-filled

symbols, dotted lines) is shown for comparison. The lines are to guide the eye.IV, V

TcU of PAMPTMA-1 is independent of polymer concentration in the range 0.1-1 mg/mL,

i.e. TcU is only determined by the concentration of LiNTf2 at a given concentration of

NaCl (figure 16). This is an observation of high importance, since it greatly simplifies the

investigation of the copolymers with varying AMPTMA-contents.

56

0.0 0.2 0.4 0.6 0.8 1.0

30

40

50

60

70

80

90T

cU (

°C)

Polymer concentration (mg/mL)

4.5 mM

5.3 mM

6.0 mM

7.0 mM

9.0 mM

Figure 16. TcU of PAMPTMA-1 in 100 mM NaCl with various concentrations of LiNTf2 as a

function of polymer concentration. The LiNTf2 concentration is given above each series.V

4.3.2. Effect of OTf on TcUIV

Although NTf2 is the main hydrophobic anion used to modulate the thermoresponsive

behavior in this study, also OTf, as its lithium salt (LiOTf), was studied for comparison,

first for PIL-B-2 (figure 17). It was immediately observed that more than a 20-fold

concentration of LiOTf compared to the concentration of LiNTf2 is needed to induce an

UCST-transition to PIL-B-2 (compare figures 14 and 17). Therefore, the ionic strength

brought in by LiOTf is not negligible and TcU in figure 17 is presented as a function of

total concentration of salts, not only concentration of NaCl like in figure 14.

The need for higher concentrations of LiOTf compared to NTf2 can be explained by

the higher hydrophilicity of the PIL-B-2-OTf system compared to PIL-B-2-NTf2-system.

This is seen from the fact that although both NTf2 and OTf yield water-insoluble

polycations109, the water solubility of small molecular organic salts with OTf as a counter

ion is higher by far80, 84, 465.

57

0 200 400 600 800 1000

20

40

60

80

TcU(°

C)

[LiOTf]+[NaCl] (mM)

20

25

35

50

75

100 150

Figure 17. TcU of 1 mg/mL aqueous PIL-1 with various concentrations of LiOTf (shown next to the

lines as mM) as a function of total concentration of added salts. The dashed red line connects

points with LiOTf as the only salt.IV

The need for higher concentrations allows the use of LiOTf as the only salt (dashed red

line in figure 17), i.e. it can provide high enough ionic strength on its own without turning

the polymer completely insoluble. This makes the system highly versatile as TcU for PIL-

B-2 can be positioned nearly anywhere in the liquid range of water just by using LiOTf.

The system did not display any dependence on polymer concentration. This is the case

with LiOTf as the only salt or with both LiOTf and NaCl present in the solution (figure

18). The transitions are significantly sharper with LiOTf than with LiNTf2.

Curious results can be obtained when inducing UCST-type behavior with OTf for

PMOTAI-1 (figure 19). The amount of LiOTf needed to observe a transition is high, 200

mM. This makes it possible to use LiOTf in a similar dual role to induce the phase

transition and provide the sufficient ionic strength, which was also the case with PIL-B-2.

After the initial increase and a broad maximum, TcU starts to decrease with increasing

concentration of LiOTf and eventually disappears completely. The author has no definite

explanation for the phenomenon, but perhaps OTf-ions bind to the polymer at very high

concentrations, similarly to surfactant binding to PNIPAm.306

The observed phenomenon is not caused by the lithium ions since an analogous

potassium salt (KOTf) yielded similar results (figure 19).

58

0.0 0.2 0.4 0.6 0.8 1.0

20

30

40

50

60

70

80

90T

cU(°

C)

polymer concentration (mg/mL)

25

3550

50

75

75

100

35

Figure 18. TcU as a function of PIL-B-2 concentration in various concentrations of LiOTf, given as

mM above the lines. The measurements have been conducted either with LiOTf as the only salt (■)

or keeping the total salt concentration constant at 100 mM with added NaCl (●).IV

0 200 400 600 800 1000 1200

10

20

30

40

50

60

TcU(°

C)

[OTf ] (mM)

Figure 19. Tc of 1 mg/mL PMOTAI solution as a function concentration of OTf-ions, with either

LiOTf (■) or KOTf (●).IV

59

4.3.3. Reversibility of the Counterion-Induced UCST-transitionIV, V

The reversibility of the counter-ion induced UCST transition was studied in some cases in

detail (figure 20). The samples were chosen in a way that the phase transitions occurred

far from the extremes of the studied temperature range, the initial values of TcU were

between 27 °C and 36 °C. Thus even in the case of major hysteresis, TcU could still be

observed.

It can be seen from figure 20 that the only system with significant hysteresis is

PMOTAI-1 with LiNTf2. It was observed during the sample preparation that the solutions

with LiNTf2 are slow to react, e.g. turbidity at room temperature develops only after a

couple of minutes and the transitions are generally broad. The ability of PAMPTMA-1-

NTf2 to react faster to the changes in temperature may be due to its hydrogen-bonding

amide, which keeps bound to water even at temperatures below TcU. Hydrogen bonding is

probably the reason for the narrow transitions of PAMPTMA-1 as well.

1 2 3

2

4

6

8

10

12

T

cU (

°C)

Number of Cycle

Figure 20. Difference of TcU between heating and cooling (ΔTcU ) over three cycles for 1 mg/mL

solutions of PMOTAI-1 in 750 mM NaCl with 40% (1.33 mM) of LiNTf2 (■), PIL-B-2 with 35 mM

LiOTf at total salt concentration of 100 mM (●), and PAMPTMA-1 in 500 mM NaCl with 10 mM

of LiNTf2 (▲). The cooling cycle was done always first.IV, V

All the measurements of CP-65 (figure 21) were started with a heating run and the

hysteresis is small in all cases, thus CP-65 resembles PAMPTMA-1 also in this sense. In

500 mM and 750 mM NaCl, the hysteresis is smaller than in the case of the lower

concentrations of NaCl. This indicates effective screening of electrostatic interactions.

60

For CP-65, hysteresis goes through a maximum with increasing concentration of

LiNTf2. The ion pairs are more dissociated at lower concentrations and the speeding up of

the dissolution process at higher concentrations is due to the process occurring at higher

temperatures.

30 40 50 60 70 80

-3

-2

-1

0

1

2

3

4

5

T

cU (

°C)

TcU

(°C)

Figure 21. ΔTcU as a function of TcU for CP-65 with varying concentrations of LiNTf2 in 100 mM

NaCl (●), 250 mM NaCl (▲), 500 mM NaCl (▼), and 750 mM NaCl (♦). Heating runs have been

conducted first. The dependence of TcU on LiNTf2 for each series is reported in figure 15.V

4.4. Effect of LiNTf2 on LCST BehaviorIII, V

The effect of LiNTf2 on TcL was also studied. This was done on thermosentive polymers

that contained cationic groups for interaction with NTf2-ions. The polymers were weakly

cationic PDMAEMA-1 and the CPs. When the majority of groups in the polymer are

cationic (PDMAEMA-1 at pH 6 and CP-65, see above), the UCST behavior starts to

dominate. Also the effect of LiNTf2 on nonionic PNIPAm-2 was studied for comparison.

4.4.1. NTf2 and PDMAEMA-1 at Room TemperatureIII

The original idea behind the use of PDMAEMA with LiNTf2 was that the degree of

protonation of PDMAEMA can be varied with pH and thus it resembles a copolymer with

a varying content of cationic units. Therefore pH can be used to control the strength of

61

interactions between the polymer and NTf2-ions. The LiNTf2 concentration was scaled

with concentration of repeating units in 1 mg/mL solution of PDMAEMA, which means

that 100 % corresponds to 6.36 mM. For the purpose of this thesis, the concentrations are

reported as mM, since this convention was followed in article V as well.

The possible interaction was first tested by decreasing the pH of 1 mg/mL solution of

PDMAEMA-1, containing an equimolar amount of LiNTf2 (figure 22). Evidently, the

interactions between the repeating units and NTf2-ions start to be significant at

approximately pH 9. This was also the case when the solution contained 100 mM LiCl,

which indicates that the interactions are highly selective.

5 6 7 8 9 10 11

I(a

.u)

pH

Figure 22. Intensity of scattered light as a function of pH from originally 1 mg/mL PDMAEMA

solution in 0.1 M LiCl (■) and in pure water (●) at 20 °C. The pH-intensity relationship obtained

by cycling pH (▲) is given for comparison (see figure 23). All samples contain equal

concentrations of LiNTf2 and DMAEMA repeating units.III

It was observed that the the PDMAEMA-1-LiNTf2-system is reversible and thus it can be

cycled between soluble and insoluble states by pH (figure 23). The onset pH of the

transition is very similar to that in the case when pH is monotonously decreased. Data

from figure 23 is added to figure 22 for comparison.

62

0 2 4 6 8 10

8.03

8.89

9.59

8.34

9.43

8.21

9.63

7.77

10.16

7.45

9.15

I(a.u

.)

Number of Addition

Figure 23. pH cycling experiment at 20 °C. Intensity of scattered light upon addition of varying

amounts of acid (red line) or base (blue line) to originally 1 mg/mL solution of PDMAEMA, after

addition of an equimolar amount of LiNTf2 (black line). Value of pH of the solution after each

addition is indicated next to the data point.III

The initial addition of LiNTf2 in figure 23 leads to a sudden increase of pH, although the

anion itself is not a base in this pH range.159-161 Evidently, the anion turns PDMAEMA-1

to a stronger base, which was tested by studying pH of the solution as a function of added

LiNTf2 (figure 24).

Regardless of the exact method of sample preparation, the trend in figure 24 is clear.

pH of the solution first rapidly increases and then levels approximately to 9.2 - 9.5. It can

be concluded that LiNTf2 indeed increases the basicity of PDMAEMA-1, presumably by

forming tight ion pairs and therefore efficiently screening the charges.

The range of pH where the leveling in figure 24 is observed forms a borderline in this

system. In a similar pH, the intensity of scattered light starts to increase (figure 22). This

pH-range also marks a significant change in the thermoresponsive behavior.

TcL in figure 24 shows a behavior dependent on the added amount of LiNTf2. The

initial decrease in TcL is probably due to the formation of hydrophobic ion pairs and the

later increase due to an increased charging of the polymer, caused by an increased basicity

of the polymer. The thermoresponsive behavior of these systems is discussed below.

63

0 1 2 3 4 5 6 7 8 9 10

8.6

8.8

9.0

9.2

9.4

9.6pH

[LiNTf2] (mM)

36

38

40

42

TcL (

°C)

Figure 24. pH of originally 1 mg/mL solution of PDMAEMA-1 as a function of concentration of

LiNTf2 by adding 100 mM LiNTf2 to a solution of PDMAEMA-1 (■) or preparing the solutions

separately(●). For the separately prepared solutions, TcL was also measured (▲).III

4.4.2. Effect of LiNTf2 on Thermoresponsive Behavior of PDMAEMA-1III

At pH above 6, where TcU was observed, it is possible to influence the TcL and Tmax of

PDMAEMA-1 in buffered solutions at constant pH with LiNTf2 (figure 25).

In solutions with pH 7 and pH 8 PDMAEMA-1 is charged enough to have a strong

interaction with NTf2 anion. The transition temperature decreases rapidly with increasing

concentration of LiNTf2. The exact values of TcL and Tmax for pH 7 and pH 8 differ, but

the general behavior is the same.

PDMAEMA-1 buffered to pH 9 is hardly charged at all. This is seen as a very mild

effect of increasing concentration of LiNTf2 to the transition temperatures; in this pH, the

salt can be present in much higher concentrations than at lower values of pH before

PDMAEMA-1 turns insoluble.

In addition, pH 9 is just below the borderline pH, below which the scattering intensity

starts to increase in the presence of LiNTf2 (figure 22) and to which the pH levels with

increasing concentration of LiNTf2 (figure 24). The effect of increasing basicity is

therefore probably already significant at pH 9, further reducing the steepness of the

decrease.

pH levels to 9.2-9.5 in figure 24. In figure 25, pH 10 is above this value. At pH 10, the

dominant effect caused by the addition of LiNTf2 is the increasing basicity of

PDMAEMA-1, since both TcL and Tmax increase with increasing concentration of the salt.

64

When PDMAEMA-1 becomes a stronger base at a constant pH, the degree of charging

increases, which in turn increases the transition temperatures.

0 1 2 3 4 5 6 7 8 9

10

20

30

40

50

60

70

80

90

TcL,

Tm

ax (

°C)

[LiNTf2] (mM)

0 20 40 60 80 100 120 140

n(LiNTf2) (mol-% to DMAEMA-units)

Figure 25. TcL (filled symbols, solid lines) and Tmax (empty symbols, dashed lines) as functions of

LiNTf2 concentration for 1 mg/mL PDMAEMA-1 at buffered solutions at pH 7(■), at pH 8 (●), at

pH 9 (▲), and at pH 10(▼).The lines are to guide the eye.III

4.4.3. Thermoresponsive Behavior of PDMAEMA with Varying pH and

Constant Concentration of LiNTf2 III

The previous subsection discussed the effect of varying concentration of LiNTf2 on the

phase transition temperature of PDMAEMA-1 at constant pH. It is of interest to study the

pH-dependency of TcL while keeping the concentration of LiNTf2 constant.

Based on the results shown in figures 13 and 25, the concentrations chosen were 1.91

mM (30 mol-% to DMAEMA-units) and 2.54 mM (40 mol-% to DMAEMA-units). The

rationale behind 30 mol-% was that it has a significant influence on TcL, but does not turn

PDMAEMA-1 completely insoluble at any pH (figure 25). Concentration of 40 mol-%

was chosen because it was the lowest concentration in which TcU was observed (figure

13). These two concentrations were then studied in buffered and unbuffered solutions.

With 30 mol-% of LiNTf2, TcL goes through a minimum at pH 8 in a buffered solution

of PDMAEMA-1 (figure 26). Before this, TcL decreases very fast. At higher pH values the

effect caused by the addition of LiNTf2 is less dramatic. As discussed above, this is due to

increased basicity and low degree of charging of PDMAEMA-1. The increased basicity is

the most significant effect above pH 9.3, as this is the point where TcL becomes higher

65

than in the solutions without LiNTf2. This pH was observed to mark a change in the

solution behavior of PDMAEMA-1-LiNTf2 system also in other measurements.

6 7 8 9 10 11

10

20

30

40

50

60

70

80

90

TcL(°

C)

pH

Figure 26. TcL of PDMAEMA-1 with 1.91 mM (30 mol-%) of LiNTf2. Both buffered (■) and

unbuffered (●) solutions were studied. The dashed line connects TcL-values for PDMAEMA-1

buffered to pH 9 and pH 10 without LiNTf2. The lines are to guide the eye.III

With 40 mol-% of LiNTf2 two separate areas of solubility can be observed (figure 27). In

the high pH range the behavior is qualitatively the same as with 30 mol-% solutions,

including the TcL-increasing effect of LiNTf2 at pH values above 9.3. The area of

solubility at low pH is defined mostly by TcU, but also TcL could be observed.

When one compares the buffered and unbuffered solutions at the high pH range in

figures 26 and 27, it is clear that buffering does not have any effect on TcL. The situation

changes when pH decreases: below 8.5 in an unbuffered solution it is not possible to

observe a phase transition at all. Only stable colloidal particles form, as was the case with

PMOTAI-1 and PIL-B-2 with NTf2 and without NaCl. The fact that the UCST transition is

not observable without buffering later led to the realization that NaCl is needed for

PMOTAI-1 and PIL-B-2 with NTf2 in order to induce an UCST-type behavior.

66

6 7 8 9 10 11

10

20

30

40

50

60

70

80

90

soluble

TcL, T

cU(°

C)

pH

sol.

insoluble

Figure 27. TcL (filled symbols) and TcU (empty symbols) of PDMAEMA-1 with 2.54 mM (40 mol-

%) of LiNTf2. Both buffered (■) and unbuffered (●) solutions were studied. The dashed line

connects TcL-values for PDMAEMA-1 buffered to pH 9 and pH 10 without LiNTf2. The areas of

solubility and insolubility have been marked for clarity. The lines are to guide the eye.III

4.4.4. PNIPAm and LiNTf2V

In order to discuss the effect LiNTf2 on thermosresponsive properties of the CPs, the

effect of the salt on the corresponding homopolymers needs to be studied. For PNIPAm-2

this was done by measuring Tmax in solutions with varying concentrations of LiNTf2 and

NaCl (figure 28). Similar concentrations of NaCl were used for PAMPTMA-1 (see

discussion above) and the CPs (see discussion below).

The dependencies of Tmax on the salt concentration are linear in the cases where only

one salt is added (figure 28). This is a common feature of various salts of the Hofmeister

series.303, 305, 314

The obtained slope for Tmax as a function of NaCl concentration (-14.3 °C/M) is in an

agreement with literature values of -13 °C/M and -10.3 °C/M. 303, 314 The author is not

aware of any reports on the slope of LiNTf2, but the obtained value of -39.5 °C/M is

similar to the strongest kosmotropes of the Hofmeister series. A fairly similar slope

between -33.7 °C/M and -38.0 °C/M has been observed for Na2SO4, one of the strongest

kosmotropes.314

The fact that LiNTf2 is such a strong kosmotrope is surprising, since this is commonly

a property of strongly hydrated ions with high charge densities.314 The reasons for this

anomaly would deserve a study of its own.

67

0 100 200 300 400 500 600 700 800 900 1000

5

10

15

20

25

30

35

40T

max (

°C)

[NaCl]+[LiNTf2] (mM)

Figure 28. Tmax as function total concentration of salts for 1 mg/mL PNIPAm-2-solutions

containing LiNTf2 without NaCl (■), with 100 mM NaCl (●), with 250 mM NaCl (▲), with 500

mM NaCl (▼) and with 750 mM NaCl (♦).The black line shows a linear fit for the solutions with

only LiNTf2 and the red line for the ones with only NaCl.V

It has been observed that with mixed salt solutions of potassium halides the dependency of

the transition temperature can be broken into contributions from the individual salts.303 In

the case presented in figure 28 this cannot be done, since the decrease in mixed solutions

is faster with increasing concentration of LiNTf2 than it is when using only LiNTf2. For

high molecular weight polymers, a two-stage phase transition for PNIPAm with high

concentrations of strong kosmotropes has been observed.314 PNIPAm-2 is evidently too

small for this.

When comparing the effect of LiNTf2 on PAMPTMA-1 (figure 15) and PNIPAm-2

(figure 28), it can be seen that the effect on PAMPTMA-1 is of completely different order

of magnitude. An illustrative example is that Tmax of PNIPAm-2, compared to pure water,

decreases by 3.4 °C in a 50 mM solution of LiNTf2, but 20 mM is enough to turn

PAMPTMA-1 completely insoluble in all studied NaCl concentrations. Therefore, any

effect arising from the interactions between NIPAm units and LiNTf2 can be neglected for

CPs; the effects arise only from the AMPTMA units.

4.4.5. Effect of LiNTf2 on TcL of CPsV

For the NIPAm-AMPTMA-copolymers with low AMPTMA content, i.e. CP-8, CP-17,

and CP-26, it is possible to greatly influence TcL by the concentration of LiNTf2 and to

68

further modulate this interaction by NaCl (figure 29). As a result, TcL can be changed over

a very wide range of temperatures. Tmax was also measured and it gave identical results,

which are therefore not shown here. Dependency of TcL on the polymer concentration is

insignificant.

0 2 4 6 8 10 12 14 16 18 20 22

20

30

40

50

TcL (

°C)

[LiNTf2] (mM)

CP-8

0 2 4 6 8 10 12 14 16 18 20 22

20

40

60

80

TcL (

°C)

[LiNTf2] (mM)

CP-17

0 2 4 6 8 10 12 14 16 18 20 22

20

40

60

80

TcL (

°C)

[LiNTf2] (mM)

CP-26

Figure 29. TcL as a function of LiNTf2 concentration for 1 mg/mL solution of CP-8, CP-17, and

CP-26 containing LiNTf2 without NaCl (■), with 100 mM NaCl (●), with 250 mM NaCl (▲), with

500 mM NaCl (▼) and with 750 mM NaCl (♦).The lines are to guide the eye.V

69

No member of the CP-series displays any phase transition in a salt free solution, but it is

possible to observe a LCST transition using LiNTf2 as the only salt. LiNTf2 effectively

“switches off” the charges, which leads to a copolymer of NIPAm and a comonomer with

tunable hydrophilicity or hydrophobicity. The width of the transition greatly decreases

with increasing the concentration of LiNTf2, which indicates reduced electrostatic

repulsions.

For CP-8, 250 mM NaCl is enough to screen the charges for such an extent that the

transition happens without any LiNTf2. A similar threshold value for CP-17 is 750 mM.

The AMPTMA-content of CP-26 is so high that not even 750 mM provides enough

screening to make the LCST transition observable without LiNTf2. The possibility of

modulating the thermoresponsive behavior of a copolymer of NIPAm and a strong

electrolyte by high ionic strengths has been reported in the literature.187

The threshold concentration of NaCl sets the upper limit of TcL and the addition of

LiNTf2 can only decrease it. The temperature range in which TcL can be varied is then

widest when NaCl is added only in amounts which do not as such induce the appearance

of the cloud point.

An important observation on the CPs in figure 29 is that none of the copolymers shows

an UCST-type phase transition. If the ion pairs dissociated completely at higher

temperatures one should observe an UCST transition. Thus, also in the case of the

homopolycations, some polycation-NTf2 interactions probably remain at elevated

temperatures and the TcU is a product of a slight tipping of the balance between solubility

and insolubility.

CP-46 contains nearly equal amounts of the both comonomers and correspondingly

displays both TcL and TcU, i.e. S-I-S-transtitions (figure 30). The coexistence of both

transitions is assumed to be due to the formation of ion pairs at low temperatures, which

causes a LCST-type transition. The ion pairs weaken at higher temperatures and this then

triggers an UCST-type transition. This is a delicate balance, and the transitions can be only

observed within a very narrow concentration range between complete solubility and total

insolubility.

As can be seen in figure 30, TcU shows only minor hysteresis. This was not the case

with TcL as no low-temperature redissolution could be observed under the used

experimental conditions. Very strong hysteresis has been observed by Longenecker et al.

for copolymers of HEMA and a methacrylamide analogue of AMPTMA.429 They attribute

this to hydrogen bonding, a valid theory in the present case as well. TcU is of electrostatic

origin and therefore does not show similar hysteresis.

70

7 8 9 10 11 12 13 14 15 16 17 18

10

20

30

40

50

60

70

80

90T

cL,

TcU (

°C)

[LiNTf2] (mM)

Figure 30. TcL (black), TcU on heating (red) and TcU on cooling (blue) as a function of LiNTf2

concetration for 1 mg/mL solution of CP-46 in 100 mM NaCl (●), 250 mM NaCl (▲), 500 mM

NaCl (▼), and 750 mM NaCl (♦). The lines are to guide the eye.V

It is known that the dissolution of PNIPAm may be very slow if the polymer is kept at

temperatures above its TcL for prolonged periods of time.284 The existence of a similar

phenomenon for CP-46 was studied by minimizing the time that the solution was kept at

elevated temperatures. This was done by conducting two heating runs in succession, with

a fast cooling between the measurements. This led to reversibility of the transition, at least

for the solutions with 500 mM NaCl (figure 31). The hydrogen bonds had little time to

reorganize.

It was observed that PNIPAm-2 in 500 mM NaCl behaves somewhat similarly to CP-

46. Not even 16 hours at 5 °C was enough to completely redissolve the polymer if the

cooling was slow. But with fast cooling, the system reversed back to its original state in

less than 4 hours. Analogous results were obtained for CP-8 in 10 mM LiNTf2 without any

NaCl.

71

12 13 14 15

10

20

30

40

50

60

70

80

90T

cL,

TcU (

°C)

[LiNTf2] (mM)

Figure 31. TcL (black) and TcU on heating (red) as a function of LiNTf2-concentration for 1

mg/mL solution of CP-46 in 250 mM NaCl (▲) and 500 mM NaCl (▼). After the initial

measurement (filled symbols) the samples have been quickly cooled back to 5 °C and the

measurement has been repeated (empty symbols). The lines are to guide the eye.V

4.4.6. Effect of LiNTf2 on ΔHIII, V

ΔH of the copolymers of NIPAm usually does not depend on the exact comonomer that

has been used, but rather linearly on the phase transition temperature.281, 347 Although the

dependencies are not completely linear, a similar behavior can be observed for the CPs in

figure 32. Also in this respect, the CPs behave as copolymers of NIPAm with a

comonomer with a tunable hydrophilicity or hydrophobicity. The fact that the data points

for each CP form a separate series instead of falling on exactly the same curve is probably

due to experimental error in determining the NIPAm content by NMR.

72

20 30 40 50 60 70

0

1000

2000

3000

4000

5000

6000

7000

H

(J/m

ol)

Tmax

(°C)

Figure 32. ΔH as a function of Tmax for CP-8 (black), CP-17 (red), and CP-26 (green) without

NaCl (■), with 100 mM NaCl (●), with 250 mM NaCl (▲), with 500 mM NaCl (▼), or with 750

mM NaCl (♦). The solutions contain varying amounts of LiNTf2. The enthalpies are reported per

mole of NIPAm-units.V

As already stated, ΔH of PDMAEMA decreases as the transition temperature decreases,

contrary to other LCST-polymers.386, 387 This is also the case with PDMAEMA-1 and the

relationship is almost linear in the case of solutions without LiNTf2 (figure 33). The

situation becomes more complicated with added LiNTf2, although solutions with pH 7-9

follow the same general trend.

The Tmax - ΔH behavior of PDMAEMA arises from the deprotonation of the basic

units upon the phase transition, which is an endothermic process. The conclusion is

supported by the observation that when measuring the pH of PDMAEMA-solution as a

function of temperature, the phase transition is marked by a kink towards lower pH.382

The decrease of enthalpy with the introduction of LiNTf2 at pH 7-9, see figure 33, can

then be because of the formation of tight ion pairs that efficiently screen the charges. The

practically constant ΔH of the pH 10 series would then be due to the interplay of increased

basicity and formation of ion pairs. Although the increased basicity becomes the

determining factor of the transition temperature at pH 10, it is assumed that the affinity of

PDMAEMA-1 towards NTf2-ions is greatly enhanced at the phase transition.

73

30 40 50 60 70 80 90

1000

2000

3000

4000

5000

6000

7000

H (

J/m

ol)

Tmax

(°C)

Figure 33. ΔH as a function of Tmax for 1 mg/mL solution of PDMAEMA-1 buffered at pH 7(■), at

pH 8 (●), at pH 9 (▲), and at pH 10(▼) with varying amounts of LiNTf2.The dashed line connects

the solutions without LiNTf2. The solid lines are to guide the eye. The enthalpies are reported per

mole of DMAEMA-units. The effect of LiNTf2 on Tmax was already shown in figure 25.III

NaCl and LiNTf2 have opposite effects on the Tmax - ΔH behavior of PNIPAm-2 (figure

34). If Tmax is decreased using only NaCl, ΔH slightly increases with decreasing Tmax. A

decrease has been observed for potassium halides.281 The difference can arise from the

different cations, since simulations indicate that the interaction of amide with sodium

cation is stronger than with potassium.317, 318 LiNTf2 strongly decreases ΔH along with

decreasing Tmax. Whether this is a common feature of all strong kosmotropes has not been

reported.

74

10 15 20 25 30 35 40

2000

3000

4000

5000

6000

7000

H

(J/m

ol)

Tmax

(°C)

Figure 34. ΔH as a function of Tmax for for 1 mg/mL PNIPAm-2-solutions with no added NaCl (■),

with 100 mM NaCl (●), with 250 mM NaCl (▲), with 500 mM NaCl (▼) and with 750 mM NaCl

(♦) with varying amounts of LiNTf2. The dashed line connects points without LiNTf2. The

concentration of LiNTf2 increases when moving left within each series. The effect of LiNTf2 on Tmax

was already shown in figure 28.V

75

5. Conclusions

This thesis discusses the aqueous solution properties of materials that combine features of

PILs and thermoresponsive polymers.

Block copolymers with PIL and PNIPAm blocks form complex aggregates in aqueous

solutions. This is the case for block copolymers with a hydrophobic PIL block at room

temperature and for block copolymers with a hydrophilic PIL blocks at temperatures

above the cloud point of PNIPAm. The collapse of PNIPAm causes enrichment of cationic

units on the surface of the formed aggregate in both cases. Interactions between the two

different repeating units were observed as well.

Anions that commonly turn PILs insoluble in water can be used to induce UCST

behavior for several polycations. Sufficient ionic strength is required to be able to observe

the phenomenon, either from the salt of the hydrophobic anion or from an added

electrolyte. The systems resemble copolymers of hydrophilic and hydrophobic monomers,

which in some cases also show UCST behavior.357 In the present case, the phase transition

temperature can be modified after the polymerization.

NTf2 as a counterion can be used to influence the LCST-type thermal response of

polymers containing cationic groups. This is the case for weakly cationic PDMAEMA, as

well as for copolymers of strongly cationic AMPTMA and thermosresponsive NIPAm.

When the content of charges is high, both polymers behave similarly as strong polycations

i.e. they show an UCST behavior in the presence of NTf2 ions. This is the case when pH

of the PDMAEMA solution is acidic or the AMPTMA-content in the copolymer is high.

For PDMAEMA, not only the thermoresponsive behavior is influenced but the

presence of NTf2 also turns the polymer to a stronger base. The competition between the

formation of water-insoluble ion pairs and increased basicity mark the solution behavior of

PDMAEMA in the presence of NTf2.

In an analogous fashion to the counterion-induced UCST, the phase transition of the

CPs can be influenced by the presence of NTf2 and can be further modulated by the

concentration of NaCl. NTf2 was observed to be among the strongest kosmotropes for

PNIPAm.

76

6. References

1. Matyjaszewski, K.; Tsarevsky, N. V. J. Am. Chem. Soc. 2014, 136, 6513-6533.

2. Goto, A.; Fukuda, T. Prog. Polym. Sci. 2004, 29, 329-385.

3. Matyjaszewski, K.; Gaynor, S.; Wang, J. Macromolecules 1995, 28, 2093-2095.

4. Georges, M. K.; Veregin, R. P. N.; Kazmaier, P. M.; Hamer, G. K. Macromolecules 1993, 26, 2987-2988.

5. Wang, J.; Matyjaszewski, K. J. Am. Chem. Soc. 1995, 117, 5614-5615.

6. Kato, M.; Kamigaito, M.; Sawamoto, M.; Higashimura, T. Macromolecules 1995, 28, 1721-1723.

7. Matyjaszewski, K. Macromolecules 2012, 45, 4015-4039.

8. Treat, N. J.; Sprafke, H.; Kramer, J. W.; Clark, P. G.; Barton, B. E.; Read de Alaniz, J.; Fors, B. P.; Hawker, C. J. J. Am. Chem. Soc. 2014, 136, 16096-16101.

9. Miyake, G. M.; Theriot, J. C. Macromolecules 2014, 47, 8255-8261.

10. Pan, X.; Lamson, M.; Yan, J.; Matyjaszewski, K. ACS Macro Lett. 2015, 4, 192-196.

11. Matyjaszewski, K.; Xia, J. Chem. Rev. 2001, 101, 2921-2990.

12. Kharasch, M. S.; Jensen, E. V.; Urry, W. H. Science 1945, 102, 128.

13. Asscher, M.; Vofsi, D. J. Chem. Soc. 1963, 1887-1896.

14. Eckenhoff, W. T.; Pintauer, T. Dalton Trans. 2011, 40, 4909-4917.

15. Fischer, H. Macromolecules 1997, 30, 5666-5672.

16. Tang, W.; Tsarevsky, N. V.; Matyjaszewski, K. J. Am. Chem. Soc. 2006, 128, 1598-1604.

17. Fischer, H. Chem. Rev. 2001, 101, 3581-3610.

18. Matyjaszewski, K.; Patten, T. E.; Xia, J. J. Am. Chem. Soc. 1997, 119, 674.

19. Braunecker, W. A.; Tsarevsky, N. V.; Gennaro, A.; Matyjaszewski, K. Macromolecules 2009, 42, 6348-6360.

20. Tang, W.; Kwak, Y.; Braunecker, W.; Tsarevsky, N. V.; Coote, M. L.; Matyjaszewski, K. J. Am. Chem. Soc. 2008, 130, 10702-10713.

21. Kajiwara, A.; Matyjaszewski, K.; Kamachi, M. Macromolecules 1998, 31, 5695-5701.

22. Shipp, D. A.; Matyjaszewski, K. Macromolecules 2000, 33, 1553-1559.

23. Zhang, H.; Klumperman, B.; Ming, W.; Fischer, H.; van der Linde, R. Macromolecules 2001, 34, 6169-6173.

24. Matyjaszewski, K.; Nanda, A. K.; Tang, W. Macromolecules 2005, 38, 2015-2018.

25. Jakubowski, W.; Matyjaszewski, K. Macromolecules 2005, 38, 4139-4146.

26. Jakubowski, W.; Min, K.; Matyjaszewski, K. Macromolecules 2006, 39, 39-45.

27. Matyjaszewski, K.; Coca, S.; Gaynor, S. G.; Wei, M.; Woodworth, B. E. Macromolecules 1997, 30, 7348-7350.

28. Zhang, Y.; Wang, Y.; Matyjaszewski, K. Macromolecules 2011, 44, 683-685.

29. Konkolewicz, D.; Wang, Y.; Krys, P.; Zhong, M.; Isse, A. A.; Gennaro, A.; Matyjaszewski, K. Polym. Chem. 2014, 5, 4409-4430.

30. Zhang, Y.; Wang, Y.; Peng, C.; Zhong, M.; Zhu, W.; Konkolewicz, D.; Matyjaszewski, K. Macromolecules 2012, 45, 78-86.

31. Chiefari, J.; Chong, Y. K.; Ercole, F.; Krstina, J.; Jeffery, J.; Le, T. P. T.; Mayadunne, R. T. A.; Meijs, G. F.; Moad, C. L.; Moad, G.; Rizzardo, E.; Thang, S. H. Macromolecules 1998, 31, 5559-5562.

32. Moad, G.; Rizzardo, E.; Thang, S. H. Polymer 2008, 49, 1079-1131.

77

33. Perrier, S.; Takolpuckdee, P. J. Polym. Sci. , Part A: Polym. Chem. 2005, 43, 5347-5393.

34. Lu, L.; Zhang, H.; Yang, N.; Cai, Y. Macromolecules 2006, 39, 3770-3776.

35. Bai, R.; You, Y.; Pan, C. Macromol. Rapid Commun. 2001, 22, 315-319.

36. Zhou, Y.; Zhu, J.; Zhu, X.; Cheng, Z. Radiat. Phys. Chem. 2006, 75, 485-492.

37. Guinaudeau, A.; Mazieres, S.; Wilson, D. J.; Destarac, M. Polym. Chem. 2012, 3, 81-84.

38. Moad, G.; Chiefari, J.; Chong, Y. K.; Krstina, J.; Mayadunne, R. T. A.; Postma, A.; Rizzardo, E.; Thang, S. H. Polym. Int. 2000, 49, 993-1001.

39. Kwak, Y.; Nicolay, R.; Matyjaszewski, K. Macromolecules 2008, 41, 6602-6604.

40. Kwak, Y.; Yamamura, Y.; Matyjaszewski, K. Macromol. Chem. Phys. 2010, 211, 493-500.

41. Nicolaÿ, R.; Kwak, Y. Isr. J. Chem. 2012, 52, 288-305.

42. Moad, G.; Rizzardo, E.; Thang, S. H. Aust. J. Chem. 2005, 58, 379-410.

43. Schilli, C.; Lanzendörfer, M. G.; Müller, A. H. E. Macromolecules 2002, 35, 6819-6827.

44. Toy, A. A.; Vana, P.; Davis, T. P.; Barner-Kowollik, C. Macromolecules 2004, 37, 744-751.

45. Feldermann, A.; Toy, A. A.; Davis, T. P.; Stenzel, M. H.; Barner-Kowollik, C. Polymer 2005, 46, 8448-8457.

46. Chong, Y. K.; Le, T. P. T.; Moad, G.; Rizzardo, E.; Thang, S. H. Macromolecules 1999, 32, 2071-2074.

47. Roy, D.; Ullah, A.; Sumerlin, B. S. Macromolecules 2009, 42, 7701-7708.

48. Schilli, C. M.; Zhang, M.; Rizzardo, E.; Thang, S. H.; Chong, Y. K.; Edwards, K.; Karlsson, G.; Mueller, A. H. E. Macromolecules 2004, 37, 7861-7866.

49. Moad, G.; Chong, Y. K.; Postma, A.; Rizzardo, E.; Thang, S. H. Polymer 2005, 46, 8458-8468.

50. Perrier, S.; Takolpuckdee, P.; Mars, C. A. Macromolecules 2005, 38, 2033-2036.

51. Charmot, D.; Corpart, P.; Adam, H.; Zard, S. Z.; Biadatti, T.; Bouhadir, G. Macromol. Symp. 2000, 150, 23-32.

52. Keddie, D. J.; Moad, G.; Rizzardo, E.; Thang, S. H. Macromolecules 2012, 45, 5321-5342.

53. Benaglia, M.; Chiefari, J.; Chong, Y. K.; Moad, G.; Rizzardo, E.; Thang, S. H. J. Am. Chem. Soc. 2009, 131, 6914-6915.

54. Benaglia, M.; Chen, M.; Chong, Y. K.; Moad, G.; Rizzardo, E.; Thang, S. H. Macromolecules 2009, 42, 9384-9386.

55. Chiefari, J.; Mayadunne, R. T. A.; Moad, C. L.; Moad, G.; Rizzardo, E.; Postma, A.; Skidmore, M. A.; Thang, S. H. Macromolecules 2003, 36, 2273-2283.

56. Coote, M. L.; Henry, D. J. Macromolecules 2005, 38, 1415-1433.

57. Moad, G.; Rizzardo, E.; Thang, S. H. Aust. J. Chem. 2012, 65, 985-1076.

58. Chong, Y. K.; Krstina, J.; Le, T. P. T.; Moad, G.; Postma, A.; Rizzardo, E.; Thang, S. H. Macromolecules 2003, 36, 2256-2272.

59. Seddon, K. R. J. Chem. Technol. Biotechnol. 1997, 68, 351-356.

60. Welton, T. Chem. Rev. 1999, 99, 2071-2083.

61. Earle, M. J.; Esperanca, J. M. S. S.; Gilea, M. A.; Canongia Lopes, J. N.; Rebelo, L. P. N.; Magee, J. W.; Seddon, K. R.; Widegren, J. A. Nature 2006, 439, 831-834.

62. Wilkes, J. S.; Zaworotko, M. J. J. Chem. Soc. , Chem. Commun. 1992, 965-967.

63. Wilkes, J. S. Green Chem. 2002, 4, 73-80.

78

64. Sheldon, R. Chem. Commun. 2001, 2399-2407.

65. Davis, J. H., Jr.; Fox, P. A. Chem. Commun. 2003, 1209-1212.

66. Visser, A. E.; Swatloski, R. P.; Reichert, W. M.; Mayton, R.; Sheff, S.; Wierzbicki, A.; Davis, J. H., Jr.; Rogers, R. D. Environ. Sci. Technol. 2002, 36, 2523-2529.

67. Swatloski, R. P.; Spear, S. K.; Holbrey, J. D.; Rogers, R. D. J. Am. Chem. Soc. 2002, 124, 4974-4975.

68. Xu, A.; Wang, J.; Wang, H. Green Chem. 2010, 12, 268-275.

69. Parviainen, H.; Parviainen, A.; Virtanen, T.; Kilpelainen, I.; Ahvenainen, P.; Serimaa, R.; Gronqvist, S.; Maloney, T.; Maunu, S. L. Carbohydr. Polym. 2014, 113, 67-76.

70. Visser, A. E.; Swatloski, R. P.; Reichert, W. M.; Griffin, S. T.; Rogers, R. D. Ind. Eng. Chem. Res. 2000, 39, 3596-3604.

71. Visser, A. E.; Swatloski, R. P.; Reichert, W. M.; Davis, J. H., Jr.; Rogers, R. D.; Mayton, R.; Sheff, S.; Wierzbicki, A. Chem. Commun. 2001, 135-136.

72. Zhao, H.; Xia, S.; Ma, P. J. Chem. Technol. Biotechnol. 2005, 80, 1089-1096.

73. Sengupta, A.; Mohapatra, P. K.; Iqbal, M.; Verboom, W.; Huskens, J.; Godbole, S. V. RSC Adv. 2012, 2, 7492-7500.

74. Blesic, M.; Gunaratne, H. Q. N.; Jacquemin, J.; Nockemann, P.; Olejarz, S.; Seddon, K. R.; Strauss, C. R. Green Chem. 2014, 16, 4115-4121.

75. Hallett, J. P.; Welton, T. Chem. Rev. 2011, 111, 3508-3576.

76. Boon, J. A.; Levisky, J. A.; Pflug, J. L.; Wilkes, J. S. J. Org. Chem. 1986, 51, 480-483.

77. Ranu, B. C.; Banerjee, S. Org. Lett. 2005, 7, 3049-3052.

78. Plechkova, N. V.; Seddon, K. R. Chem. Soc. Rev. 2008, 37, 123-150.

79. Bonhôte, P.; Dias, A.; Armand, M.; Papageorgiou, N.; Kalyanasundaram, K.; Grätzel, M. Inorg. Chem. 1996, 35, 1168-1178.

80. Papaiconomou, N.; Yakelis, N.; Salminen, J.; Bergman, R.; Prausnitz, J. M. J. Chem. Eng. Data 2006, 51, 1389-1393.

81. Ngo, H. L.; LeCompte, K.; Hargens, L.; McEwen, A. B. Thermochim. Acta 2000, 357-358, 97-102.

82. Huddleston, J. G.; Visser, A. E.; Reichert, W. M.; Willauer, H. D.; Broker, G. A.; Rogers, R. D. Green Chem. 2001, 3, 156-164.

83. Pernak, J.; Czepukowicz, A.; Pozniak, R. Ind. Eng. Chem. Res. 2001, 40, 2379-2383.

84. Freire, M. G.; Santos, L. M. N. B. F.; Fernandes, A. M.; Coutinho, J. A. P.; Marrucho, I. M. Fluid Phase Equilib. 2007, 261, 449-454.

85. Freire, M. G.; Neves, C. M. S. S.; Carvalho, P. J.; Gardas, R. L.; Fernandes, A. M.; Marrucho, I. M.; Santos, L. M. N. B. F.; Coutinho, J. A. P. J. Phys. Chem. B 2007, 111, 13082-13089.

86. Stillinger, F. H. Science 1980, 209, 451-457.

87. Baldwin, R. L. Proc. Natl. Acad. Sci. U. S. A. 1986, 83, 8069-8072.

88. Privalov, P. L.; Gill, S. J. Pure Appl. Chem. 1989, 61, 1097-1104.

89. Hummer, G.; Garde, S.; Garcia, A. E.; Paulaitis, M. E.; Pratt, L. R. J. Phys. Chem. B 1998, 102, 10469-10482.

90. Scatena, L. F.; Brown, M. G.; Richmond, G. L. Science 2001, 292, 908-912.

91. Southall, N. T.; Dill, K. A.; Haymet, A. D. J. J. Phys. Chem. B 2002, 106, 521-533.

92. Fumino, K.; Wulf, A.; Ludwig, R. Angew. Chem. , Int. Ed. 2008, 47, 8731-8734.

93. Wulf, A.; Fumino, K.; Ludwig, R. Angew. Chem. , Int. Ed. 2010, 49, 449-453, S449/1-S449/14.

94. Noack, K.; Schulz, P. S.; Paape, N.; Kiefer, J.; Wasserscheid, P.; Leipertz, A. Phys. Chem. Chem. Phys. 2010, 12, 14153-14161.

79

95. Wulf, A.; Fumino, K.; Ludwig, R. J. Phys. Chem. A 2010, 114, 685-686.

96. Hunt, P. A. J. Phys. Chem. B 2007, 111, 4844-4853.

97. Fumino, K.; Peppel, T.; Geppert-Rybczynska, M.; Zaitsau, D. H.; Lehmann, J. K.; Verevkin, S. P.; Koeckerling, M.; Ludwig, R. Phys. Chem. Chem. Phys. 2011, 13, 14064-14075.

98. Lassegues, J.; Grondin, J.; Cavagnat, D.; Johansson, P. J. Phys. Chem. A 2009, 113, 6419-6421.

99. Lassegues, J.; Grondin, J.; Cavagnat, D.; Johansson, P. J. Phys. Chem. A 2010, 114, 687-688.

100. Buffeteau, T.; Grondin, J.; Danten, Y.; Lassegues, J. J. Phys. Chem. B 2010, 114, 7587-7592.

101. Dong, K.; Zhang, S. Chem. --Eur. J. 2012, 18, 2748-2761.

102. Fumino, K.; Ludwig, R. J. Mol. Liq. 2014, 192, 94-102.

103. Dupont, J. Acc. Chem. Res. 2011, 44, 1223-1231.

104. Yuan, J.; Mecerreyes, D.; Antonietti, M. Prog. Polym. Sci. 2013, 38, 1009-1036.

105. Ohno, H.; Ito, K. Chem. Lett. 1998, 751-752.

106. Ohno, H. Macromol. Symp. 2007, 249-250, 551-556.

107. Nishimura, N.; Ohno, H. Polymer 2014, 55, 3289-3297.

108. Marcilla, R.; Blazquez, J. A.; Rodriguez, J.; Pomposo, J. A.; Mecerreyes, D. J. Polym. Sci. , Part A: Polym. Chem. 2003, 42, 208-212.

109. Marcilla, R.; Blazquez, J. A.; Fernandez, R.; Grande, H.; Pomposo, J. A.; Mecerreyes, D. Macromol. Chem. Phys. 2005, 206, 299-304.

110. Marcilla, R.; Ochoteco, E.; Pozo-Gonzalo, C.; Grande, H.; Pomposo, J. A.; Mecerreyes, D. Macromol. Rapid Commun. 2005, 26, 1122-1126.

111. Marcilla, R.; Sanchez-Paniagua, M.; Lopez-Ruiz, B.; Lopez-Cabarcos, E.; Ochoteco, E.; Grande, H.; Mecerreyes, D. J. Polym. Sci. , Part A: Polym. Chem. 2006, 44, 3958-3965.

112. Marcilla, R.; Pozo-Gonzalo, C.; Rodriguez, J.; Alduncin, J. A.; Pomposo, J. A.; Mecerreyes, D. Synth. Met. 2006, 156, 1133-1138.

113. Marcilla, R.; Curri, M. L.; Cozzoli, P. D.; Martinez, M. T.; Loinaz, I.; Grande, H.; Pomposo, J. A.; Mecerreyes, D. Small 2006, 2, 507-512.

114. Texter, J. Macromol. Rapid Commun. 2012, 33, 1996-2014.

115. Alfassi, Z. B.; Huie, R. E.; Milman, B. L.; Neta, P. Anal. Bioanal. Chem. 2003, 377, 159-164.

116. Ye, Y.; Elabd, Y. A. Polymer 2011, 52, 1309-1317.

117. Green, M. D.; Salas-de la Cruz, D.; Ye, Y.; Layman, J. M.; Elabd, Y. A.; Winey, K. I.; Long, T. E. Macromol. Chem. Phys. 2011, 212, 2522-2528.

118. Nakamura, K.; Fukao, K.; Inoue, T. Macromolecules 2012, 45, 3850-3858.

119. Tang, J.; Tang, H.; Sun, W.; Radosz, M.; Shen, Y. J. Polym. Sci. , Part A: Polym. Chem. 2005, 43, 5477-5489.

120. Xue, H.; Verma, R.; Shreeve, J. M. J. Fluorine Chem. 2006, 127, 159-176.

121. Freire, M. G.; Carvalho, P. J.; Gardas, R. L.; Marrucho, I. M.; Santos, L. M. N. B. F.; Coutinho, J. A. P. J. Phys. Chem. B 2008, 112, 1604-1610.

122. Shvedene, N. V.; Borovskaya, S. V.; Sviridov, V. V.; Ismailova, E. R.; Pletnev, I. V. Anal. Bioanal. Chem. 2005, 381, 427-430.

123. Chapeaux, A.; Simoni, L. D.; Stadtherr, M. A.; Brennecke, J. F. J. Chem. Eng. Data 2007, 52, 2462-2467.

124. Ranke, J.; Othman, A.; Fan, P.; Mueller, A. Int. J. Mol. Sci. 2009, 10, 1271-1289.

80

125. Sun, J.; Forsyth, M.; MacFarlane, D. R. J. Phys. Chem. B 1998, 102, 8858-8864.

126. Krossing, I.; Slattery, J. M.; Daguenet, C.; Dyson, P. J.; Oleinikova, A.; Weingaertner, H. J. Am. Chem. Soc. 2006, 128, 13427-13434.

127. Nakamura, K.; Saiwaki, T.; Fukao, K.; Inoue, T. Macromolecules 2011, 44, 7719-7726.

128. Nakamura, K.; Fukao, K. Polymer 2013, 54, 3306-3313.

129. Shaplov, A. S.; Lozinskaya, E. I.; Ponkratov, D. O.; Malyshkina, I. A.; Vidal, F.; Aubert, P.; Okatova, O. V.; Pavlov, G. M.; Komarova, L. I.; Wandrey, C.; Vygodskii, Y. S. Electrochim. Acta 2011, 57, 74-90.

130. Mi, H.; Jiang, Z.; Kong, J. Polymers 2013, 5, 1203-1214, 12.

131. Vijayakrishna, K.; Jewrajka, S. K.; Ruiz, A.; Marcilla, R.; Pomposo, J. A.; Mecerreyes, D.; Taton, D.; Gnanou, Y. Macromolecules 2008, 41, 6299-6308.

132. Vijayakrishna, K.; Mecerreyes, D.; Gnanou, Y.; Taton, D. Macromolecules 2009, 42, 5167-5174.

133. Adzima, B. J.; Taylor, S. C.; He, H.; Luebke, D. R.; Matyjaszewski, K.; Nulwala, H. B. J. Polym. Sci. , Part A: Polym. Chem. 2014, 52, 417-423.

134. Cammarata, L.; Kazarian, S. G.; Salter, P. A.; Welton, T. Phys. Chem. Chem. Phys. 2001, 3, 5192-5200.

135. Deetlefs, M.; Hardacre, C.; Nieuwenhuyzen, M.; Padua, A. A. H.; Sheppard, O.; Soper, A. K. J. Phys. Chem. B 2006, 110, 12055-12061.

136. Bodo, E.; Gontrani, L.; Caminiti, R.; Plechkova, N. V.; Seddon, K. R.; Triolo, A. J. Phys. Chem. B 2010, 114, 16398-16407.

137. Katsyuba, S. A.; Vener, M. V.; Zvereva, E. E.; Fei, Z.; Scopelliti, R.; Laurenczy, G.; Yan, N.; Paunescu, E.; Dyson, P. J. J. Phys. Chem. B 2013, 117, 9094-9105.

138. Crowhurst, L.; Mawdsley, P. R.; Perez-Arlandis, J. M.; Salter, P. A.; Welton, T. Phys. Chem. Chem. Phys. 2003, 5, 2790-2794.

139. Golding, J. J.; MacFarlane, D. R.; Spiccia, L.; Golding, J. J.; Forsyth, M.; Skelton, B. W.; White, A. H. Chem. Commun. 1998, 1593-1594.

140. Fox, P. A.; Griffin, S. T.; Reichert, W. M.; Salter, E. A.; Smith, A. B.; Tickell, M. D.; Wicker, B. F.; Cioffi, E. A.; Davis, J. H., Jr.; Rogers, R. D.; Wierzbicki, A. Chem. Commun. 2005, 3679-3681.

141. Tsuzuki, S.; Tokuda, H.; Hayamizu, K.; Watanabe, M. J. Phys. Chem. B 2005, 109, 16474-16481.

142. Bini, R.; Bortolini, O.; Chiappe, C.; Pieraccini, D.; Siciliano, T. J. Phys. Chem. B 2007, 111, 598-604.

143. Fernandes, A. M.; Rocha, M. A. A.; Freire, M. G.; Marrucho, I. M.; Coutinho, J. A. P.; Santos, L. M. N. B. F. J. Phys. Chem. B 2011, 115, 4033-4041.

144. Matsumoto, K.; Hagiwara, R. J. Fluorine Chem. 2007, 128, 317-331.

145. Freire, M. G.; Neves, C. M. S. S.; Shimizu, K.; Bernardes, C. E. S.; Marrucho, I. M.; Coutinho, J. A. P.; Lopes, J. N. C.; Rebelo, L. P. N. J. Phys. Chem. B 2010, 114, 15925-15934.

146. Martins, M. A. R.; Neves, C. M. S. S.; Kurnia, K. A.; Santos, L. M. N. B. F.; Freire, M. G.; Pinho, S. P.; Coutinho, J. A. P. Fluid Phase Equilib. 2014, 381, 28-35.

147. Johansson, P.; Gejji, S. P.; Tegenfeldt, J.; Lindgren, J. Electrochim. Acta 1998, 43, 1375-1379.

148. Herstedt, M.; Smirnov, M.; Johansson, P.; Chami, M.; Grondin, J.; Servant, L.; Lassegues, J. C. J. Raman Spectrosc. 2005, 36, 762-770.

149. Fujii, K.; Fujimori, T.; Takamuku, T.; Kanzaki, R.; Umebayashi, Y.; Ishiguro, S. J. Phys. Chem. B 2006, 110, 8179-8183.

81

150. Moschovi, A. M.; Dracopoulos, V.; Nikolakis, V. J. Phys. Chem. B 2014, 118, 8673-8683.

151. Lassegues, J. C.; Grondin, J.; Holomb, R.; Johansson, P. J. Raman Spectrosc. 2007, 38, 551-558.

152. Shukla, M.; Noothalapati, H.; Shigeto, S.; Saha, S. Vib. Spectrosc. 2014, 75, 107-117.

153. Faria, L. F. O.; Matos, J. R.; Ribeiro, M. C. C. J. Phys. Chem. B 2012, 116, 9238-9245.

154. Fujii, K.; Soejima, Y.; Kyoshoin, Y.; Fukuda, S.; Kanzaki, R.; Umebayashi, Y.; Yamaguchi, T.; Ishiguro, S.; Takamuku, T. J. Phys. Chem. B 2008, 112, 4329-4336.

155. Appetecchi, G. B.; Croce, F.; Scrosati, B. Electrochim. Acta 1995, 40, 991-997.

156. Sakaebe, H.; Matsumoto, H. Electrochem. Commun. 2003, 5, 594-598.

157. Garcia, B.; Lavallee, S.; Perron, G.; Michot, C.; Armand, M. Electrochim. Acta 2004, 49, 4583-4588.

158. Stephan, A. M.; Nahm, K. S. Polymer 2006, 47, 5952-5964.

159. Koppel, I. A.; Taft, R. W.; Anvia, F.; Zhu, S.; Hu, L.; Sung, K.; DesMarteau, D. D.; Yagupolskii, L. M.; Yagupolskii, Y. L.; et al J. Am. Chem. Soc. 1994, 116, 3047-3057.

160. Foropoulos, J., Jr.; DesMarteau, D. D. Inorg. Chem. 1984, 23, 3720-3723.

161. Kutt, A.; Rodima, T.; Saame, J.; Raamat, E.; Maemets, V.; Kaljurand, I.; Koppel, I. A.; Garlyauskayte, R. Y.; Yagupolskii, Y. L.; Yagupolskii, L. M.; Bernhardt, E.; Willner, H.; Leito, I. J. Org. Chem. 2011, 76, 391-395.

162. Haas, A.; Klare, C.; Betz, P.; Bruckmann, J.; Krueger, C.; Tsay, Y. -.; Aubke, F. Inorg. Chem. 1996, 35, 1918-1925.

163. Rey, I.; Johansson, P.; Lindgren, J.; Lassegues, J. C.; Grondin, J.; Servant, L. J. Phys. Chem. A 1998, 102, 3249-3258.

164. Stoyanov, E. S.; Kim, K.; Reed, C. A. J. Phys. Chem. A 2004, 108, 9310-9315.

165. Yan, F.; Texter, J. Chem. Commun. 2006, 2696-2698.

166. Ma, X.; Ashaduzzaman, M.; Kunitake, M.; Crombez, R.; Texter, J.; Slater, L.; Mourey, T. Langmuir 2011, 27, 7148-7157.

167. Hu, X.; Huang, J.; Zhang, W.; Li, M.; Tao, C.; Li, G. Adv. Mater. 2008, 20, 4074-4078.

168. Texter, J. Macromol. Rapid Commun. 2012, 33, 1996-2014.

169. Wamser, C. A. J. Am. Chem. Soc. 1948, 70, 1209-1215.

170. Platford, R. F. Can. J. Chem. 1971, 49, 709-711.

171. Mesmer, R. E.; Palen, K. M.; Baes, C. F.,Jr Inorg. Chem. 1973, 12, 89-95.

172. Swatloski, R. P.; Holbrey, J. D.; Rogers, R. D. Green Chem. 2003, 5, 361-363.

173. Pham, T. P. T.; Cho, C.; Yun, Y. Water Res. 2010, 44, 352-372.

174. Pham, T. P. T.; Cho, C.; Vijayaraghavan, K.; Min, J.; Yun, Y. Environ. Toxicol. Chem. 2008, 27, 1583-1589.

175. Archer, D. G.; Widegren, J. A.; Kirklin, D. R.; Magee, J. W. J. Chem. Eng. Data 2005, 50, 1484-1491.

176. Fernandez-Galan, R.; Manzano, B. R.; Otero, A.; Lanfranchi, M.; Pellinghelli, M. A. Inorg. Chem. 1994, 33, 2309-2312.

177. Lu, Y.; King, F. L.; Duckworth, D. C. J. Am. Soc. Mass Spectrom. 2006, 17, 939-944.

178. Freire, M. G.; Neves, C. M. S. S.; Marrucho, I. M.; Coutinho, J. A. P.; Fernandes, A. M. J. Phys. Chem. A 2010, 114, 3744-3749.

179. Lu, J.; Yan, F.; Texter, J. Prog. Polym. Sci. 2009, 34, 431-448.

180. Green, O.; Grubjesic, S.; Lee, S.; Firestone, M. A. Polym. Rev. 2009, 49, 339-360.

82

181. Green, M. D.; Long, T. E. Polym. Rev. 2009, 49, 291-314.

182. Anderson, E. B.; Long, T. E. Polymer 2010, 51, 2447-2454.

183. Yuan, J.; Antonietti, M. Polymer 2011, 52, 1469-1482.

184. Mecerreyes, D. Prog. Polym. Sci. 2011, 36, 1629-1648.

185. Qiu, B.; Lin, B.; Yan, F. Polym. Int. 2013, 62, 335-337.

186. Men, Y.; Kuzmicz, D.; Yuan, J. Curr. Opin. Colloid Interface Sci. 2014, 19, 76-83.

187. Soll, S.; Antonietti, M.; Yuan, J. ACS Macro Lett. 2012, 1, 84-87.

188. Antonietti, M.; Shen, Y.; Nakanishi, T.; Manuelian, M.; Campbell, R.; Gwee, L.; Elabd, Y. A.; Tambe, N.; Crombez, R.; Texter, J. ACS Appl. Mater. Interfaces 2010, 2, 649-653.

189. Fukushima, T.; Kosaka, A.; Ishimura, Y.; Yamamoto, T.; Takigawa, T.; Ishii, N.; Aida, T. Science 2003, 300, 2072-2075.

190. Men, Y.; Li, X.; Antonietti, M.; Yuan, J. Polym. Chem. 2012, 3, 871-873.

191. Grygiel, K.; Chabanne, L.; Men, Y.; Yuan, J. Macromol. Symp. 2014, 342, 67-77.

192. Texter, J.; Ager, D.; Vasantha, V. A.; Crombez, R.; England, D.; Ma, X.; Maniglia, R.; Tambe, N. Chem. Lett. 2012, 41, 1377-1379.

193. Ager, D.; Arjunan Vasantha, V.; Crombez, R.; Texter, J. ACS Nano 2014, 8, 11191-11205.

194. Kim, T. Y.; Tung, T. T.; Lee, T. H.; Kim, J. E.; Suh, K. S. Chem. - Asian J. 2010, 5, 256-260.

195. Kim, T.; Lee, H.; Kim, J.; Suh, K. S. ACS Nano 2010, 4, 1612-1618.

196. Gao, H.; Zhang, S.; Lu, F.; Jia, H.; Zheng, L. Colloid Polym. Sci. 2012, 290, 1785-1791.

197. Texter, J. Curr. Opin. Colloid Interface Sci. 2014, 19, 163-174.

198. Gracia, R.; Vijayakrishna, K.; Mecerreyes, D. React. Funct. Polym. 2014, 79, 54-58.

199. Prabhu Charan, K. T.; Pothanagandhi, N.; Vijayakrishna, K.; Sivaramakrishna, A.; Mecerreyes, D.; Sreedhar, B. Eur. Polym. J. 2014, 60, 114-122.

200. Tollan, C. M.; Marcilla, R.; Pomposo, J. A.; Rodriguez, J.; Aizpurua, J.; Molina, J.; Mecerreyes, D. ACS Appl. Mater. Interfaces 2009, 1, 348-352.

201. Giordano, C.; Yang, W.; Lindemann, A.; Crombez, R.; Texter, J. Colloids Surf. , A 2011, 374, 84-87.

202. Batra, D.; Seifert, S.; Varela, L. M.; Liu, A. C. Y.; Firestone, M. A. Adv. Funct. Mater. 2007, 17, 1279-1287.

203. Lee, J.; Aida, T. Chem. Commun. 2011, 47, 6757-6762.

204. Fukushima, T.; Kosaka, A.; Yamamoto, Y.; Aimiya, T.; Notazawa, S.; Takigawa, T.; Inabe, T.; Aida, T. Small 2006, 2, 554-560.

205. Fukushima, T.; Aida, T. Chem. - Eur. J. 2007, 13, 5048-5058.

206. Throckmorton, J. A.; Watters, A. L.; Geng, X.; Palmese, G. R. Compos. Sci. Technol. 2013, 86, 38-44.

207. Prasad, K.; Kadokawa, J. Polym. Compos. 2010, 31, 799-806.

208. Murakami, M.; Kaneko, Y.; Kadokawa, J. Carbohydr. Polym. 2007, 69, 378-381.

209. Kadokawa, J.; Murakami, M.; Kaneko, Y. Compos. Sci. Technol. 2008, 68, 493-498.

210. Takegawa, A.; Murakami, M.; Kaneko, Y.; Kadokawa, J. Polym. Compos. 2009, 30, 1837-1841.

211. Setoyama, M.; Kato, T.; Yamamoto, K.; Kadokawa, J. J. Polym. Environ. 2013, 21, 795-801.

212. Mizumo, T.; Watanabe, T.; Matsumi, N.; Ohno, H. Polym. Adv. Technol. 2008, 19, 1445-1450.

83

213. Döbbelin, M.; Marcilla, R.; Pozo-Gonzalo, C.; Mecerreyes, D. J. Mater. Chem. 2010, 20, 7613-7622.

214. Lee, T. H.; Kim, T. Y.; Duong, H. T. T.; Kim, J. E.; Suh, K. S. Synth. Met. 2009, 159, 2453-2457.

215. Kim, T. Y.; Lee, T. H.; Kim, J. E.; Kasi, R. M.; Sung, C. S. P.; Suh, K. S. J. Polym. Sci. , Part A: Polym. Chem. 2008, 46, 6872-6879.

216. Kim, T. Y.; Suh, M.; Kwon, S. J.; Lee, T. H.; Kim, J. E.; Lee, Y. J.; Kim, J. H.; Hong, M. P.; Suh, K. S. Macromol. Rapid Commun. 2009, 30, 1477-1482.

217. Pozo-Gonzalo, C.; Marcilla, R.; Salsamendi, M.; Mecerreyes, D.; Pomposo, J. A.; Rodriguez, J.; Bolink, H. J. J. Polym. Sci. , Part A: Polym. Chem. 2008, 46, 3150-3154.

218. Kwon, S. J.; Kim, T. Y.; Lee, B. S.; Lee, T. H.; Kim, J. E.; Suh, K. S. Synth. Met. 2010, 160, 1092-1096.

219. Zhao, J.; Yan, F.; Chen, Z.; Diao, H.; Chu, F.; Yu, S.; Lu, J. J. Polym. Sci. , Part A: Polym. Chem. 2009, 47, 746-753.

220. Burns, C. T.; Lee, S.; Seifert, S.; Firestone, M. A. Polym. Adv. Technol. 2008, 19, 1369-1382.

221. Ho, H. A.; Leclerc, M. J. Am. Chem. Soc. 2003, 125, 4412-4413.

222. Döbbelin, M.; Pozo-Gonzalo, C.; Marcilla, R.; Blanco, R.; Segura, J. L.; Pomposo, J. A.; Mecerreyes, D. J. Polym. Sci. , Part A: Polym. Chem. 2009, 47, 3010-3021.

223. Zhang, W.; Li, Y.; Lin, C.; An, Q.; Tao, C.; Gao, Y.; Li, G. J. Polym. Sci. , Part A: Polym. Chem. 2008, 46, 4151-4161.

224. de Jong, M. P.; van IJzendoorn, L. J.; de Voigt, M. J. A. Appl. Phys. Lett. 2000, 77, 2255-2257.

225. Kawano, K.; Pacios, R.; Poplavskyy, D.; Nelson, J.; Bradley, D. D. C.; Durrant, J. R. Sol. Energy Mater. Sol. Cells 2006, 90, 3520-3530.

226. Grossiord, N.; Kroon, J. M.; Andriessen, R.; Blom, P. W. M. Org. Electron. 2012, 13, 432-456.

227. Norrman, K.; Madsen, M. V.; Gevorgyan, S. A.; Krebs, F. C. J. Am. Chem. Soc. 2010, 132, 16883-16892.

228. Cros, S.; de Bettignies, R.; Berson, S.; Bailly, S.; Maisse, P.; Lemaitre, N.; Guillerez, S. Sol. Energy Mater. Sol. Cells 2011, 95, S65-S69.

229. Muldoon, M. J.; Gordon, C. M. J. Polym. Sci. , Part A: Polym. Chem. 2004, 42, 3865-3869.

230. Yang, J.; Qiu, L.; Liu, B.; Peng, Y.; Yan, F.; Shang, S. J. Polym. Sci. , Part A: Polym. Chem. 2011, 49, 4531-4538.

231. Yuan, J.; Soll, S.; Drechsler, M.; Mueller, A. H. E.; Antonietti, M. J. Am. Chem. Soc. 2011, 133, 17556-17559.

232. Soll, S.; Antonietti, M.; Yuan, J. Polymer 2014, 55, 3415-3422.

233. Tokuda, M.; Sanada, T.; Shindo, T.; Suzuki, T.; Minami, H. Langmuir 2014, 30, 3406-3412.

234. Sanchez-Paniagua Lopez, M.; Mecerreyes, D.; Lopez-Cabarcos, E.; Lopez-Ruiz, B. Biosens. Bioelectron. 2006, 21, 2320-2328.

235. Tokuda, M.; Minami, H.; Mizuta, Y.; Yamagami, T. Macromol. Rapid Commun. 2012, 33, 1130-1134.

236. Tokuda, M.; Minami, H. J. Colloid Interface Sci. 2013, 398, 120-125.

237. Yuan, J.; Antonietti, M. Macromolecules 2011, 44, 744-750.

238. Rahman, M. T.; Barikbin, Z.; Badruddoza, A. Z. M.; Doyle, P. S.; Khan, S. A. Langmuir 2013, 29, 9535-9543.

84

239. Xiong, Y.; Wang, H.; Wang, R.; Yan, Y.; Zheng, B.; Wang, Y. Chem. Commun. 2010, 46, 3399-3401.

240. Xiong, Y.; Wang, Y.; Wang, H.; Wang, R. Polym. Chem. 2011, 2, 2306-2315.

241. Sui, X.; Hempenius, M. A.; Vancso, G. J. J. Am. Chem. Soc. 2012, 134, 4023-4025.

242. Stancik, C. M.; Lavoie, A. R.; Schuetz, J.; Achurra, P. A.; Lindner, P.; Gast, A. P.; Waymouth, R. M. Langmuir 2004, 20, 596-605.

243. Texter, J.; Vasantha, V. A.; Crombez, R.; Maniglia, R.; Slater, L.; Mourey, T. Macromol. Rapid Commun. 2012, 33, 69-74.

244. Guo, J.; Zhou, Y.; Qiu, L.; Yuan, C.; Yan, F. Polym. Chem. 2013, 4, 4004-4009.

245. Qiu, H.; Sawada, T.; Jiang, S.; Ihara, H. Mater. Lett. 2010, 64, 1653-1655.

246. Ye, Q.; Gao, T.; Wan, F.; Yu, B.; Pei, X.; Zhou, F.; Xue, Q. J. Mater. Chem. 2012, 22, 13123-13131.

247. Bi, W.; Tian, M.; Row, K. H. Analyst 2012, 137, 2017-2020.

248. Qiu, H.; Mallik, A. K.; Takafuji, M.; Jiang, S.; Ihara, H. Analyst 2012, 137, 2553-2555.

249. Qiu, H.; Mallik, A. K.; Sawada, T.; Takafuji, M.; Ihara, H. Chem. Commun. 2012, 48, 1299-1301.

250. Yuan, J.; Wunder, S.; Warmuth, F.; Lu, Y. Polymer 2012, 53, 43-49.

251. Zhao, Q.; Fellinger, T.; Antonietti, M.; Yuan, J. Macromol Rapid Commun 2012, 33, 1149-1153.

252. Tokuda, M.; Shindo, T.; Minami, H. Langmuir 2013, 29, 11284-11289.

253. Bo, X.; Bai, J.; Ju, J.; Guo, L. J. Power Sources 2011, 196, 8360-8365.

254. Pourjavadi, A.; Doulabi, M. Solid State Ionics 2014, 257, 32-37.

255. Yan, F.; Texter, J. Angew. Chem. , Int. Ed. 2007, 46, 2440-2443.

256. Gu, H.; Texter, J. Polymer 2014, 55, 3378-3384.

257. Carlisle, T. K.; McDanel, W. M.; Cowan, M. G.; Noble, R. D.; Gin, D. L. Chem. Mater. 2014, 26, 1294-1296.

258. Batra, D.; Hay, D. N. T.; Firestone, M. A. Chem. Mater. 2007, 19, 4423-4431.

259. Penzel, E.; Rieger, J.; Schneider, H. A. Polymer 1997, 38, 325-337.

260. Grunlan, J. C.; Ma, Y.; Grunlan, M. A.; Gerberich, W. W.; Francis, L. F. Polymer 2001, 42, 6913-6921.

261. Uschanov, P.; Heiskanen, N.; Mononen, P.; Maunu, S. L.; Koskimies, S. Prog. Org. Coat. 2008, 63, 92-99.

262. Chen, H.; Choi, J.; Salas-de la Cruz, D.; Winey, K. I.; Elabd, Y. A. Macromolecules 2009, 42, 4809-4816.

263. Jovanovski, V.; Marcilla, R.; Mecerreyes, D. Macromol. Rapid Commun. 2010, 31, 1646-1651.

264. Tomé, L. C.; Aboudzadeh, M. A.; Rebelo, L. P. N.; Freire, C. S. R.; Mecerreyes, D.; Marrucho, I. M. J. Mater. Chem. A 2013, 1, 10403-10411.

265. Jovanovski, V.; Cabanero, G.; Grande, H.; Mecerreyes, D. Macromol. Symp. 2012, 311, 77-82.

266. Seuring, J.; Agarwal, S. Macromol. Rapid Commun. 2012, 33, 1898-1920.

267. Aseyev, V.; Tenhu, H.; Winnik, F. M. Adv. Polym. Sci. 2011, 242, 29-89.

268. Heskins, M.; Guillet, J. E. J. Macromol. Sci. , Chem. 1968, 2, 1441-1455.

269. Pelton, R. J. Colloid Interface Sci. 2010, 348, 673-674.

270. Kubota, K.; Fujishige, S.; Ando, I. J. Phys. Chem. 1990, 94, 5154-5158.

271. Wu, C.; Zhou, S. Macromolecules 1995, 28, 5388-5390.

85

272. Wu, C.; Wang, X. Phys. Rev. Lett. 1998, 80, 4092-4094.

273. Wang, X.; Qiu, X.; Wu, C. Macromolecules 1998, 31, 2972-2976.

274. Schild, H. G.; Tirrell, D. A. J. Phys. Chem. 1990, 94, 4352-4356.

275. Cho, E. C.; Lee, J.; Cho, K. Macromolecules 2003, 36, 9929-9934.

276. Sun, B.; Lin, Y.; Wu, P.; Siesler, H. W. Macromolecules 2008, 41, 1512-1520.

277. Deshmukh, S. A.; Sankaranarayanan, S. K. R. S.; Suthar, K.; Mancini, D. C. J. Phys. Chem. B 2012, 116, 2651-2663.

278. Philipp, M.; Kyriakos, K.; Silvi, L.; Lohstroh, W.; Petry, W.; Krueger, J. K.; Papadakis, C. M.; Mueller-Buschbaum, P. J. Phys. Chem. B 2014, 118, 4253-4260.

279. Maeda, Y.; Higuchi, T.; Ikeda, I. Langmuir 2000, 16, 7503-7509.

280. Maeda, Y.; Nakamura, T.; Ikeda, I. Macromolecules 2001, 34, 1391-1399.

281. Maeda, Y.; Higuchi, T.; Ikeda, I. Langmuir 2001, 17, 7535-7539.

282. Katsumoto, Y.; Tanaka, T.; Sato, H.; Ozaki, Y. J. Phys. Chem. A 2002, 106, 3429-3435.

283. Cheng, H.; Shen, L.; Wu, C. Macromolecules 2006, 39, 2325-2329.

284. Van Durme, K.; Van Assche, G.; Van Mele, B. Macromolecules 2004, 37, 9596-9605.

285. Tiktopulo, E. I.; Bychkova, V. E.; Ricka, J.; Ptitsyn, O. B. Macromolecules 1994, 27, 2879-2882.

286. Okada, Y.; Tanaka, F. Macromolecules 2005, 38, 4465-4471.

287. Tiktopulo, E. I.; Uversky, V. N.; Lushchik, V. B.; Klenin, S. I.; Bychkova, V. E.; Ptitsyn, O. B. Macromolecules 1995, 28, 7519-7524.

288. Dawson, K. A.; Gorelov, A. V.; Timoshenko, E. G.; Kuznetsov, Y. A.; Du Chesne, A. Physica A 1997, 244, 68-80.

289. Ushakova, A. S.; Govorun, E. N.; Khokhlov, A. R. J. Phys. : Condens. Matter 2006, 18, 915-930.

290. Kujawa, P.; Tanaka, F.; Winnik, F. M. Macromolecules 2006, 39, 3048-3055.

291. Chan, K.; Pelton, R.; Zhang, J. Langmuir 1999, 15, 4018-4020.

292. Aseyev, V.; Hietala, S.; Laukkanen, A.; Nuopponen, M.; Confortini, O.; Du Prez, F. E.; Tenhu, H. Polymer 2005, 46, 7118-7131.

293. Kujawa, P.; Aseyev, V.; Tenhu, H.; Winnik, F. M. Macromolecules 2006, 39, 7686-7693.

294. Wu, C.; Li, W.; Zhu, X. X. Macromolecules 2004, 37, 4989-4992.

295. Chuang, J.; Grosberg, A. Y.; Tanaka, T. J. Chem. Phys. 2000, 112, 6434-6442.

296. Tong, Z.; Zeng, F.; Zheng, X.; Sato, T. Macromolecules 1999, 32, 4488-4490.

297. Otake, K.; Inomata, H.; Konno, M.; Saito, S. Macromolecules 1990, 23, 283-289.

298. Principi, T.; Goh, C. C. E.; Liu, R. C. W.; Winnik, F. M. Macromolecules 2000, 33, 2958-2966.

299. Xia, Y.; Burke, N. A. D.; Stöver, H. D. H. Macromolecules 2006, 39, 2275-2283.

300. Chung, J. E.; Yokoyama, M.; Aoyagi, T.; Sakurai, Y.; Okano, T. J. Controlled Release 1998, 53, 119-130.

301. Ye, J.; Xu, J.; Hu, J.; Wang, X.; Zhang, G.; Liu, S.; Wu, C. Macromolecules 2008, 41, 4416-4422.

302. Qiu, X. P.; Koga, T.; Tanaka, F.; Winnik, F. M. Sci. China: Chem. 2013, 56, 56-64.

303. Freitag, R.; Garret-Flaudy, F. Langmuir 2002, 18, 3434-3440.

304. Nuopponen, M.; Kalliomäki, K.; Laukkanen, A.; Hietala, S.; Tenhu, H. J. Polym. Sci. , Part A: Polym. Chem. 2007, 46, 38-46.

86

305. Zhang, Y.; Furyk, S.; Bergbreiter, D. E.; Cremer, P. S. J. Am. Chem. Soc. 2005, 127, 14505-14510.

306. Schild, H. G.; Tirrell, D. A. Langmuir 1991, 7, 665-671.

307. Lee, L.; Cabane, B. Macromolecules 1997, 30, 6559-6566.

308. Patel, T.; Ghosh, G.; Yusa, S.; Bahadur, P. J. Dispersion Sci. Technol. 2011, 32, 1111-1118.

309. Winnik, F. M.; Ringsdorf, H.; Venzmer, J. Macromolecules 1990, 23, 2415-2416.

310. Schild, H. G.; Muthukumar, M.; Tirrell, D. A. Macromolecules 1991, 24, 948-952.

311. Costa, R. O. R.; Freitas, R. F. S. Polymer 2002, 43, 5879-5885.

312. Scherzinger, C.; Schwarz, A.; Bardow, A.; Leonhard, K.; Richtering, W. Curr. Opin. Colloid Interface Sci. 2014, 19, 84-94.

313. Zhang, Y.; Cremer, P. S. Curr. Opin. Chem. Biol. 2006, 10, 658-663.

314. Zhang, Y.; Furyk, S.; Sagle, L. B.; Cho, Y.; Bergbreiter, D. E.; Cremer, P. S. J. Phys. Chem. C 2007, 111, 8916-8924.

315. Shechter, I.; Ramon, O.; Portnaya, I.; Paz, Y.; Livney, Y. D. Macromolecules 2010, 43, 480-487.

316. Zhang, Y.; Cremer, P. S. Annu. Rev. Phys. Chem. 2010, 61, 63-83.

317. Du, H.; Wickramasinghe, R.; Qian, X. J. Phys. Chem. B 2010, 114, 16594-16604.

318. Du, H.; Wickramasinghe, S. R.; Qian, X. J. Phys. Chem. B 2013, 117, 5090-5101.

319. Heyda, J.; Dzubiella, J. J. Phys. Chem. B 2014, 118, 10979-10988.

320. Qiu, X.; Tanaka, F.; Winnik, F. M. Macromolecules 2007, 40, 7069-7071.

321. Qiu, X.; Winnik, F. M. Macromol. Symp. 2009, 278, 10-13.

322. Xu, J.; Ye, J.; Liu, S. Macromolecules 2007, 40, 9103-9110.

323. Satokawa, Y.; Shikata, T.; Tanaka, F.; Qiu, X.; Winnik, F. M. Macromolecules 2009, 42, 1400-1403.

324. Ray, B.; Okamoto, Y.; Kamigaito, M.; Sawamoto, M.; Seno, K.; Kanaoka, S.; Aoshima, S. Polym. J. 2005, 37, 234-237.

325. Katsumoto, Y.; Kubosaki, N. Macromolecules 2008, 41, 5955-5956.

326. Ito, M.; Ishizone, T. J. Polym. Sci. , Part A: Polym. Chem. 2006, 44, 4832-4845.

327. Hirano, T.; Okumura, Y.; Kitajima, H.; Seno, M.; Sato, T. J. Polym. Sci. , Part A: Polym. Chem. 2006, 44, 4450-4460.

328. Chang, K.; Dicke, Z. T.; Taite, L. J. J. Polym. Sci. , Part A: Polym. Chem. 2012, 50, 976-985.

329. Afroze, F.; Nies, E.; Berghmans, H. J. Mol. Struct. 2000, 554, 55-68.

330. Fujishige, S.; Kubota, K.; Ando, I. J. Phys. Chem. 1989, 93, 3311-3313.

331. Xia, Y.; Yin, X.; Burke, N. A. D.; Stöver, H. D. H. Macromolecules 2005, 38, 5937-5943.

332. Pamies, R.; Zhu, K.; Kjøniksen, A.; Nyström, B. Polym. Bull. 2009, 62, 487-502.

333. Kujawa, P.; Segui, F.; Shaban, S.; Diab, C.; Okada, Y.; Tanaka, F.; Winnik, F. M. Macromolecules 2006, 39, 341-348.

334. Duan, Q.; Miura, Y.; Narumi, A.; Shen, X.; Sato, S.; Satoh, T.; Kakuchi, T. J. Polym. Sci. , Part A: Polym. Chem. 2006, 44, 1117-1124.

335. Furyk, S.; Zhang, Y.; Ortiz-Acosta, D.; Cremer, P. S.; Bergbreiter, D. E. J. Polym. Sci. , Part A: Polym. Chem. 2006, 44, 1492-1501.

336. Chung, J. E.; Yokoyama, M.; Suzuki, K.; Aoyagi, T.; Sakurai, Y.; Okano, T. Colloids Surf. , B 1997, 9, 37-48.

87

337. Cammas, S.; Suzuki, K.; Sone, C.; Sakurai, Y.; Kataoka, K.; Okano, T. J. Controlled Release 1997, 48, 157-164.

338. Kohori, F.; Sakai, K.; Aoyagi, T.; Yokoyama, M.; Sakurai, Y.; Okano, T. J. Controlled Release 1998, 55, 87-98.

339. Nuopponen, M.; Ojala, J.; Tenhu, H. Polymer 2004, 45, 3643-3650.

340. Takei, Y. G.; Aoki, T.; Sanui, K.; Ogata, N.; Okano, T.; Sakurai, Y. Bioconjugate Chem. 1993, 4, 341-346.

341. Kawasaki, H.; Sasaki, S.; Maeda, H. J. Phys. Chem. B 1997, 101, 5089-5093.

342. Liu, H.; Avoce, D.; Song, Z.; Zhu, X. X. Macromol. Rapid Commun. 2001, 22, 675-680.

343. Maeda, T.; Kanda, T.; Yonekura, Y.; Yamamoto, K.; Aoyagi, T. Biomacromolecules 2006, 7, 545-549.

344. Shen, Z.; Terao, K.; Maki, Y.; Dobashi, T.; Ma, G.; Yamamoto, T. Colloid Polym. Sci. 2006, 284, 1001-1007.

345. Weng, Y.; Ding, Y.; Zhang, G. J Phys Chem B 2006, 110, 11813-11817.

346. Heyda, J.; Soll, S.; Yuan, J.; Dzubiella, J. Macromolecules 2014, 47, 2096-2102.

347. Feil, H.; Bae, Y. H.; Feijen, J.; Kim, S. W. Macromolecules 1993, 26, 2496-2500.

348. Maeda, Y.; Yamamoto, H.; Ikeda, I. Langmuir 2001, 17, 6855-6859.

349. Maeda, T.; Yamamoto, K.; Aoyagi, T. J. Colloid Interface Sci. 2006, 302, 467-474.

350. Seuring, J.; Agarwal, S. ACS Macro Lett. 2013, 2, 597-600.

351. Lowe, A. B.; McCormick, C. L. Chem. Rev. 2002, 102, 4177-4189.

352. Chen, L.; Honma, Y.; Mizutani, T.; Liaw, D. -.; Gong, J. P.; Osada, Y. Polymer 1999, 41, 141-147.

353. Mary, P.; Bendejacq, D. D.; Labeau, M.; Dupuis, P. J. Phys. Chem. B 2007, 111, 7767-7777.

354. Hildebrand, V.; Laschewsky, A.; Zehm, D. J. Biomater. Sci. , Polym. Ed. 2014, 25, 1602-1618.

355. Woodfield, P. A.; Zhu, Y.; Pei, Y.; Roth, P. J. Macromolecules 2014, 47, 750-762.

356. Glatzel, S.; Laschewsky, A.; Lutz, J. Macromolecules 2011, 44, 413-415.

357. Seuring, J.; Agarwal, S. Macromolecules 2012, 45, 3910-3918.

358. Flory, P. J.; Osterheld, J. E. J. Phys. Chem. 1954, 58, 653-661.

359. Aoki, T.; Nakamura, K.; Sanui, K.; Kikuchi, A.; Okano, T.; Sakurai, Y.; Ogata, N. Polym. J. 1999, 31, 1185-1188.

360. Mishra, V.; Jung, S.; Jeong, H. M.; Lee, H. Polym. Chem. 2014, 5, 2411-2416.

361. Seuring, J.; Agarwal, S. Macromol. Chem. Phys. 2010, 211, 2109-2117.

362. Liu, F.; Seuring, J.; Agarwal, S. J. Polym. Sci. , Part A: Polym. Chem. 2012, 50, 4920-4928.

363. Liu, F.; Seuring, J.; Agarwal, S. Polym. Chem. 2013, 4, 3123-3131.

364. Glatzel, S.; Badi, N.; Päch, M.; Laschewsky, A.; Lutz, J. Chem. Commun. 2010, 46, 4517-4519.

365. Seuring, J.; Bayer, F. M.; Huber, K.; Agarwal, S. Macromolecules 2012, 45, 374-384.

366. Shimada, N.; Ino, H.; Maie, K.; Nakayama, M.; Kano, A.; Maruyama, A. Biomacromolecules 2011, 12, 3418-3422.

367. Shimada, N.; Nakayama, M.; Kano, A.; Maruyama, A. Biomacromolecules 2013, 14, 1452-1457.

368. Noh, M.; Mok, Y.; Nakayama, D.; Jang, S.; Lee, S.; Kim, T.; Lee, Y. Polymer 2013, 54, 5338-5344.

88

369. Meiswinkel, G.; Ritter, H. Macromol. Rapid Commun. 2013, 34, 1026-1031.

370. Meiswinkel, G.; Ritter, H. Macromol. Chem. Phys. 2013, 214, 2835-2840.

371. Pineda-Contreras, B. A.; Liu, F.; Agarwal, S. J. Polym. Sci. , Part A: Polym. Chem. 2014, 52, 1878-1884.

372. Endo, N.; Shirota, H.; Horie, K. Macromol. Rapid Commun. 2001, 22, 593-597.

373. Deng, L.; Wang, C.; Li, Z.; Liang, D. Macromolecules 2010, 43, 3004-3010.

374. Sudre, G.; Tran, Y.; Creton, C.; Hourdet, D. Polymer 2012, 53, 379-385.

375. Litmanovich, E. A.; Chernikova, E. V.; Stoychev, G. V.; Zakharchenko, S. O. Macromolecules 2010, 43, 6871-6876.

376. Choi, H. S.; Huh, K. M.; Ooya, T.; Yui, N. J. Am. Chem. Soc. 2003, 125, 6350-6351.

377. Choi, H. S.; Ooya, T.; Sasaki, S.; Yui, N. Macromolecules 2003, 36, 5342-5347.

378. Gonsior, N.; Ritter, H. Macromol. Chem. Phys. 2012, 213, 382-388.

379. van de Wetering, P.; Zuidam, N. J.; van Steenbergen, M. J.; van der Houwen, O. A. G. J.; Underberg, W. J. M.; Hennink, W. E. Macromolecules 1998, 31, 8063-8068.

380. Bütün, V.; Armes, S. P.; Billingham, N. C. Polymer 2001, 42, 5993-6008.

381. Georgiou, T. K.; Vamvakaki, M.; Patrickios, C. S.; Yamasaki, E. N.; Phylactou, L. A. Biomacromolecules 2004, 5, 2221-2229.

382. Plamper, F. A.; Ruppel, M.; Schmalz, A.; Borisov, O.; Ballauff, M.; Müller, A. H. E. Macromolecules 2007, 40, 8361-8366.

383. Schallon, A.; Synatschke, C. V.; Pergushov, D. V.; Jérôme, V.; Müller, A. H. E.; Freitag, R. Langmuir 2011, 27, 12042-12051.

384. Lee, H.; Son, S. H.; Sharma, R.; Won, Y. J. Phys. Chem. B 2011, 115, 844-860.

385. Fournier, D.; Hoogenboom, R.; Thijs, H. M. L.; Paulus, R. M.; Schubert, U. S. Macromolecules 2007, 40, 915-920.

386. Niskanen, J.; Karesoja, M.; Rossi, T.; Tenhu, H. Polym. Chem. 2011, 2, 2027-2036.

387. Niskanen, J.; Wu, C.; Ostrowski, M.; Fuller, G. G.; Hietala, S.; Tenhu, H. Macromolecules 2013, 46, 2331-2340.

388. Schmalz, A.; Hanisch, M.; Schmalz, H.; Mueller, A. H. E. Polymer 2010, 51, 1213-1217.

389. Thavanesan, T.; Herbert, C.; Plamper, F. A. Langmuir 2014, 30, 5609-5619.

390. Plamper, F. A.; Schmalz, A.; Ballauff, M.; Müller, A. H. E. J. Am. Chem. Soc. 2007, 129, 14538-14539.

391. Plamper, F. A.; McKee, J. R.; Laukkanen, A.; Nykänen, A.; Walther, A.; Ruokolainen, J.; Aseyev, V.; Tenhu, H. Soft Matter 2009, 5, 1812-1821.

392. Plamper, F. A.; Walther, A.; Müller, A. H. E.; Ballauff, M. Nano Lett. 2007, 7, 167-171.

393. Plamper, F. A.; Murtomäki, L.; Walther, A.; Kontturi, K.; Tenhu, H. Macromolecules 2009, 42, 7254-7257.

394. Jia, X.; Chen, D.; Jiang, M. Chem. Commun. 2006, 1736-1738.

395. Hu, J.; Ge, Z.; Zhou, Y.; Zhang, Y.; Liu, S. Macromolecules 2010, 43, 5184-5187.

396. Hunley, M. T.; England, J. P.; Long, T. E. Macromolecules 2010, 43, 9998-10005.

397. Moreno, M.; Ali Aboudzadeh, M.; Barandiaran, M. J.; Mecerreyes, D. J. Polym. Sci. , Part A: Polym. Chem. 2012, 50, 1049-1053.

398. Kohno, Y.; Saita, S.; Men, Y.; Yuan, J.; Ohno, H. Polym. Chem. 2015, 6, 2163-2178.

399. Yoshimitsu, H.; Kanazawa, A.; Kanaoka, S.; Aoshima, S. Macromolecules 2012, 45, 9427-9434.

400. Dyson, P. J.; Ellis, D. J.; Welton, T. Can. J. Chem. 2001, 79, 705-708.

89

401. Najdanovic-Visak, V.; Esperanca, J. M. S. S.; Rebelo, L. P. N.; Nunes da Ponte, M.; Guedes, H. J. R.; Seddon, K. R.; Szydlowski, J. Phys. Chem. Chem. Phys. 2002, 4, 1701-1703.

402. Rebelo, L. P. N.; Najdanovic-Visak, V.; Visak, Z. P.; Nunes da Ponte, M.; Szydlowski, J.; Cerdeirina, C. A.; Troncoso, J.; Romani, L.; Esperanca, J. M. S. S.; Guedes, H. J. R.; de Sousa, H. C. Green Chem. 2004, 6, 369-381.

403. Nockemann, P.; Binnemans, K.; Thijs, B.; Parac-Vogt, T. N.; Merz, K.; Mudring, A.; Menon, P. C.; Rajesh, R. N.; Cordoyiannis, G.; Thoen, J.; Leys, J.; Glorieux, C. J. Phys. Chem. B 2009, 113, 1429-1437.

404. Kohno, Y.; Ohno, H. Aust. J. Chem. 2012, 65, 91-94.

405. Kohno, Y.; Deguchi, Y.; Ohno, H. Chem. Commun. 2012, 48, 11883-11885.

406. Li, W.; Wu, P. Polym. Chem. 2014, 5, 5578-5590.

407. Men, Y.; Schlaad, H.; Voelkel, A.; Yuan, J. Polym. Chem. 2014, 5, 3719-3724.

408. Ziółkowski, B.; Diamond, D. Chem. Commun. 2013, 49, 10308-10310.

409. Men, Y.; Schlaad, H.; Yuan, J. ACS Macro Lett. 2013, 2, 456-459.

410. Kohno, Y.; Deguchi, Y.; Inoue, N.; Ohno, H. Aust. J. Chem. 2013, 66, 1393-1398.

411. Amajjahe, S.; Ritter, H. Macromolecules 2008, 41, 3250-3253.

412. Fukumoto, K.; Ohno, H. Angew. Chem. , Int. Ed. 2007, 46, 1852-1855.

413. Kohno, Y.; Ohno, H. Phys. Chem. Chem. Phys. 2012, 14, 5063-5070.

414. Illescas, J.; Casu, M.; Alzari, V.; Nuvoli, D.; Scorciapino, M. A.; Sanna, R.; Sanna, V.; Mariani, A. J. Polym. Sci. , Part A: Polym. Chem. 2014, 52, 3521-3532.

415. Seo, J.; Hwang, J.; Shin, U. S. RSC Adv. 2014, 4, 26738-26747.

416. Kawasaki, H.; Sasaki, S.; Maeda, H. J. Phys. Chem. B 1997, 101, 4184-4187.

417. Kawasaki, H.; Sasaki, S.; Maeda, H.; Nishinari, K. Langmuir 2000, 16, 3195-3199.

418. Szczubiałka, K.; Loska, R.; Nowakowska, M. J. Polym. Sci. , Part A: Polym. Chem. 2001, 39, 2784-2792.

419. Mun, G. A.; Nurkeeva, Z. S.; Khutoryanskiy, V. V.; Sergaziyev, A. D.; Rosiak, J. M. Radiat. Phys. Chem. 2002, 65, 67-70.

420. Tauer, K.; Weber, N.; Texter, J. Chem. Commun. 2009, , 6065-6067.

421. Weber, N.; Texter, J.; Tauer, K. Macromol. Symp. 2011, 302, 224-234.

422. Yuan, J.; Schlaad, H.; Giordano, C.; Antonietti, M. Eur. Polym. J. 2011, 47, 772-781.

423. Mori, H.; Yahagi, M.; Endo, T. Macromolecules 2009, 42, 8082-8092.

424. Wang, Z.; Lai, H.; Wu, P. Soft Matter 2012, 8, 11644-11653.

425. Yu, R.; Tauer, K. Polym. Chem. 2014, 5, 5644-5655.

426. Men, Y.; Drechsler, M.; Yuan, J. Macromol. Rapid Commun. 2013, 34, 1721-1727.

427. Zhou, X.; Zhou, Y.; Nie, J.; Ji, Z.; Xu, J.; Zhang, X.; Du, B. ACS Appl. Mater. Interfaces 2014, 6, 4498-4513.

428. Mori, T.; Nakashima, M.; Fukuda, Y.; Minagawa, K.; Tanaka, M.; Maeda, Y. Langmuir 2006, 22, 4336-4342.

429. Longenecker, R.; Mu, T.; Hanna, M.; Burke, N. A. D.; Stöver, H. D. H. Macromolecules 2011, 44, 8962-8971.

430. Chang, Y.; Chen, W.; Yandi, W.; Shih, Y.; Chu, W.; Liu, Y.; Chu, C.; Ruaan, R.; Higuchi, A. Biomacromolecules 2009, 10, 2092-2100.

431. Bokias, G.; Staikos, G.; Iliopoulos, I. Polymer 2000, 41, 7399-7405.

432. Fang, J.; Bian, F.; Shen, W. J. Appl. Polym. Sci. 2008, 110, 3373-3378.

433. Idziak, I.; Avoce, D.; Lessard, D.; Gravel, D.; Zhu, X. X. Macromolecules 1999, 32, 1260-1263.

90

434. Yamamoto, S.; Pietrasik, J.; Matyjaszewski, K. Macromolecules 2008, 41, 7013-7020.

435. Weaver, J. V. M.; Bannister, I.; Robinson, K. L.; Bories-Azeau, X.; Armes, S. P.; Smallridge, M.; McKenna, P. Macromolecules 2004, 37, 2395-2403.

436. Mori, H.; Kato, I.; Saito, S.; Endo, T. Macromolecules 2010, 43, 1289-1298.

437. Ding, S.; Tang, H.; Radosz, M.; Shen, Y. J. Polym. Sci. Part A 2004, 42, 5794-5801.

438. Mori, H.; Iwaya, H.; Nagai, A.; Endo, T. Chem. Commun. 2005, , 4872-4874.

439. Reddy, P. M.; Venkatesu, P. J. Phys. Chem. B 2011, 115, 4752-4757.

440. Wang, Z.; Wu, P. RSC Adv. 2012, 2, 7099-7108.

441. Reddy, P. M.; Umapathi, R.; Venkatesu, P. Phys. Chem. Chem. Phys. 2014, 16, 10708-10718.

442. Debeljuh, N. J.; Sutti, A.; Barrow, C. J.; Byrne, N. J. Phys. Chem. B 2013, 117, 8430-8435.

443. Pamies, R.; Zhu, K.; Volden, S.; Kjøniksen, A.; Karlsson, G.; Glomm, W. R.; Nyström, B. J. Phys. Chem. C 2010, 114, 21960-21968.

444. Marinova, K. G.; Alargova, R. G.; Denkov, N. D.; Velev, O. D.; Petsev, D. N.; Ivanov, I. B.; Borwankar, R. P. Langmuir 1996, 12, 2045-2051.

445. Tandon, V.; Bhagavatula, S. K.; Nelson, W. C.; Kirby, B. J. Electrophoresis 2008, 29, 1092-1101.

446. Tandon, V.; Kirby, B. J. Electrophoresis 2008, 29, 1102-1114.

447. Jena, K. C.; Scheu, R.; Roke, S. Angew. Chem. , Int. Ed. 2012, 51, 12938-12940.

448. Beattie, J. K.; Gray-Weale, A. Angew. Chem. , Int. Ed. 2012, 51, 12941-12942.

449. O'Brien, R. W.; Beattie, J. K.; Djerdjev, A. M. J. Colloid Interface Sci. 2014, 420, 70-73.

450. Wu, Y.; Li, Q.; Deng, F.; Liang, X.; Liu, H. Langmuir 2014, 30, 1926-1931.

451. Roger, K.; Cabane, B. Angew. Chem. , Int. Ed. 2012, 51, 5625-5628.

452. Roger, K.; Cabane, B. Angew. Chem. , Int. Ed. 2012, 51, 12943-12945.

453. Parry, A. L.; Bomans, P. H. H.; Holder, S. J.; Sommerdijk, N. A. J. M.; Biagini, S. C. G. Angew. Chem. , Int. Ed. 2008, 47, 8859-8862.

454. McKenzie, B. E.; Nudelman, F.; Bomans, P. H. H.; Holder, S. J.; Sommerdijk, N. A. J. M. J. Am. Chem. Soc. 2010, 132, 10256-10259.

455. Holder, S. J.; Sommerdijk, N. A. J. M. Polym. Chem. 2011, 2, 1018-1028.

456. McKenzie, B. E.; de Visser, J. F.; Friedrich, H.; Wirix, M. J. M.; Bomans, P. H. H.; de With, G.; Holder, S. J.; Sommerdijk, N. A. J. M. Macromolecules 2013, 46, 9845-9848.

457. Steinschulte, A. A.; Schulte, B.; Erberich, M.; Borisov, O. V.; Plamper, F. A. ACS Macro Lett. 2012, 1, 504-507.

458. Steinschulte, A. A.; Schulte, B.; Ruetten, S.; Eckert, T.; Okuda, J.; Moeller, M.; Schneider, S.; Borisov, O. V.; Plamper, F. A. Phys. Chem. Chem. Phys. 2014, 16, 4917-4932.

459. Earle, M. J.; Gordon, C. M.; Plechkova, N. V.; Seddon, K. R.; Welton, T. Anal. Chem. 2007, 79, 758-764.

460. Page, K. A.; England, D.; Texter, J. ACS Macro Lett. 2012, 1, 1398-1402.

461. England, D.; Yan, F.; Texter, J. Langmuir 2013, 29, 12013-12024.

462. Liu, B.; Kazlauciunas, A.; Guthrie, J. T.; Perrier, S. Macromolecules 2005, 38, 2131-2136.

463. Bannister, I.; Billingham, N. C.; Armes, S. P.; Rannard, S. P.; Findlay, P. Macromolecules 2006, 39, 7483-7492.

91

464. Wang, W.; Zheng, Y.; Roberts, E.; Duxbury, C. J.; Ding, L.; Irvine, D. J.; Howdle, S. M. Macromolecules 2007, 40, 7184-7194.

465. O'Mahony, A. M.; Silvester, D. S.; Aldous, L.; Hardacre, C.; Compton, R. G. J. Chem. Eng. Data 2008, 53, 2884-2891.